ConTeXt tool for enabling comments in PDF ?

ConTeXt tool for enabling comments in PDF ?

[Steffen Wolfrum]

Hi,

in the MacOSX-TeX-list (mainly on LaTeX) I just read a discussion on "Comments in PDF" (by AcrobatReader7).

Do we have a ConTeXt tool which can enable users of e.g. AdobeReader 7 to add comments to PDF files ?
Or is it true that this "comments enabled flag" can only be set for PDFs generated by Acrobat -- and only by the original author?


Steffen



Henning Hraban Ramm <hraban@fiee.net> wrote:

> There's a lot of new or enhanced features for us prepress people, e.g. 
> for Reader Extensions you don't need this expensive server product any 
> more, that means, if you own Acrobat 7 Professional you can enable the 
> correction tools in Reader for your document.

Re: ConTeXt tool for enabling comments in PDF ?

[Mark Smith]

Steffen Wolfrum wrote:

>Hi,
>
>in the MacOSX-TeX-list (mainly on LaTeX) I just read a discussion on 
>"Comments in PDF" (by AcrobatReader7).

I was involved in that discussion.

>Do we have a ConTeXt tool which can enable users of e.g. AdobeReader 7 to 
>add comments to PDF files ?
>Or is it true that this "comments enabled flag" can only be set for PDFs 
>generated by Acrobat -- and only by the original author?

Quick summary of the thread:

The general opinion was that this is effectively an Acrobat-only feature. In fact, it seems that one needs Acrobat 6 or 7 Pro to enable commenting in this way and that (at least on Mac) the "commmenting author" needs Reader 7 to be able to participate. That said, it was suggested that (though ill-advisable) the Acrobat security model could probably be readily breached in this respect by third party tools. I wonder if either (or both) of these:

<http://shop.pdf-office.com/product_info.php?products_id=34&osCsid=a1241e335670fc0b939a8c03b77536f2>

<http://shop.pdf-office.com/product_info.php?products_id=47&osCsid=a1241e335670fc0b939a8c03b77536f2>

allow it ? Setting comments is not AFAICS mentioned in the blurb, but similar tricks are. OTOH an academic license for 7 Pro is not *that* much more expensive.

mark.

Re: ConTeXt tool for enabling comments in PDF ?

[Mark Smith]

I wrote:

(regarding enabling comments in PDFs)

>I wonder if either (or both) of these:
>
><http://shop.pdf-office.com/product_info.php?products_id=34&osCsid=
>a1241e335670fc0b939a8c03b77536f2>
>
><http://shop.pdf-office.com/product_info.php?products_id=47&osCsid=
>a1241e335670fc0b939a8c03b77536f2>
>
>allow it ?

well, I took the plunge and applied for demos of both. It looks like neither does the trick.

mark.

Re: ConTeXt tool for enabling comments in PDF ?

[Henning Hraban Ramm]

Am 05.01.2005 um 12:03 schrieb Mark Smith:
> The general opinion was that this is effectively an Acrobat-only 
> feature. In fact, it seems that one needs Acrobat 6 or 7 Pro to enable 
> commenting in this way and that (at least on Mac) the "commmenting 
> author" needs Reader 7 to be able to participate. That said, it was

The other way round:
You need Acrobat 7 Pro to enable "Reader Extensions" for a document, 
afterwards you can comment PDFs with Reader 6 or 7

Grüßlis vom Hraban!
---
http://www.fiee.net/texnique/
http://contextgarden.net

Re: ConTeXt tool for enabling comments in PDF ?

[Mark Smith]

Henning Hraban Ramm wrote:

>Am 05.01.2005 um 12:03 schrieb Mark Smith:
>> The general opinion was that this is effectively an Acrobat-only 
>> feature. In fact, it seems that one needs Acrobat 6 or 7 Pro to enable 
>> commenting in this way and that (at least on Mac) the "commmenting 
>> author" needs Reader 7 to be able to participate. That said, it was
>
>The other way round:
>You need Acrobat 7 Pro to enable "Reader Extensions" for a document, 
>afterwards you can comment PDFs with Reader 6 or 7

Same way round actually. 7 Pro enables the enabling of comments (a paraphrase of "enables commenting") in a document. The "commenting author" is the one who writes the comments and needs (as I said) on Mac (I believe), Reader 7. We are saying the same thing.

The meat of the thread was more about the how-to's and why-not's of enabling "Reader Extensions" w/o 7 Pro.

Re: ConTeXt tool for enabling comments in PDF ?

[Hans Hagen]

Mark Smith wrote:
> Henning Hraban Ramm wrote:
> 
> 
>>Am 05.01.2005 um 12:03 schrieb Mark Smith:
>>
>>>The general opinion was that this is effectively an Acrobat-only 
>>>feature. In fact, it seems that one needs Acrobat 6 or 7 Pro to enable 
>>>commenting in this way and that (at least on Mac) the "commmenting 
>>>author" needs Reader 7 to be able to participate. That said, it was
>>
>>The other way round:
>>You need Acrobat 7 Pro to enable "Reader Extensions" for a document, 
>>afterwards you can comment PDFs with Reader 6 or 7
> 
> 
> Same way round actually. 7 Pro enables the enabling of comments (a paraphrase of "enables commenting") in a document. The "commenting author" is the one who writes the comments and needs (as I said) on Mac (I believe), Reader 7. We are saying the same thing.
> 
> The meat of the thread was more about the how-to's and why-not's of enabling "Reader Extensions" w/o 7 Pro.

as far as i know, the readers 6/7 have more options than advertised and these 
can be turned on by plug-ins and probably special document settings (hidden by 
the encryption); has to do with this ebook stuff

Hans


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Re: ConTeXt tool for enabling comments in PDF ?

[Hans Hagen]

Henning Hraban Ramm wrote:
> Am 05.01.2005 um 12:03 schrieb Mark Smith:
> 
>> The general opinion was that this is effectively an Acrobat-only 
>> feature. In fact, it seems that one needs Acrobat 6 or 7 Pro to enable 
>> commenting in this way and that (at least on Mac) the "commmenting 
>> author" needs Reader 7 to be able to participate. That said, it was
> 
> 
> The other way round:
> You need Acrobat 7 Pro to enable "Reader Extensions" for a document, 
> afterwards you can comment PDFs with Reader 6 or 7

can you make me a small document that has the reader extensions enabled?

Hans


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                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
      tel: 038 477 53 69 | fax: 038 477 53 74 | www.pragma-ade.com
                                              | www.pragma-pod.nl
-----------------------------------------------------------------

Re: ConTeXt tool for enabling comments in PDF ?

[Henning Hraban Ramm]

Am 06.01.2005 um 11:02 schrieb Hans Hagen:
>> You need Acrobat 7 Pro to enable "Reader Extensions" for a document, 
>> afterwards you can comment PDFs with Reader 6 or 7
> can you make me a small document that has the reader extensions 
> enabled?

I'd like to, but there's no german Acrobat 7 yet, and I won't buy an 
english one.

Grüßlis vom Hraban!
---
http://www.fiee.net/texnique/
http://contextgarden.net

Re: ConTeXt tool for enabling comments in PDF ?

[Mark Smith]

Henning Hraban Ramm wrote:

>I'd like to, but there's no german Acrobat 7 yet, and I won't buy an 
>english one.

Interesting. I'm in Germany too and am currently having trouble getting an international English version of 7 Pro at the education price. A German one is on offer.

Re: ConTeXt tool for enabling comments in PDF ?

[Hans Hagen]

Steffen Wolfrum wrote:
> Hi,
> 
> in the MacOSX-TeX-list (mainly on LaTeX) I just read a discussion on "Comments in PDF" (by AcrobatReader7).
> 
> Do we have a ConTeXt tool which can enable users of e.g. AdobeReader 7 to add comments to PDF files ?
> Or is it true that this "comments enabled flag" can only be set for PDFs generated by Acrobat -- and only by the original author?

you can read comments in the reader, but not add them; but you can use tex to 
add them and the reader will recognize them

\setupinteraction[state=start]

\starttext

\startcomment should work in older readers as well \stopcomment

\input bryson

\stoptext


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               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
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                                              | www.pragma-pod.nl
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Re: ConTeXt tool for enabling comments in PDF ?

[Mark Smith]

Hans Hagen wrote:

>you can read comments in the reader, but not add them; but you can use tex 
>to add them and the reader will recognize them

Hope I'm not misrepresenting anyone here, but I think the utility of this function for [Con|La]TeX[t] users is not so much in being able to add comments oneself in the input file(s) (though this has its uses), but in being able to send a draft PDF to non-TeX-savvy co-authors +/or editors and giving them (more or less) free reign to add their comments to it, if possible w/o completely destroying any security. (I'm currently having to generate RTF or "Word HTML" drafts for such purposes.)

mark.

Re: ConTeXt tool for enabling comments in PDF ?

[Vit Zyka]

> Do we have a ConTeXt tool which can enable users of e.g. AdobeReader 7 to add comments to PDF files ?
> Or is it true that this "comments enabled flag" can only be set for PDFs generated by Acrobat -- and only by the original author?

I have played with this yesterday evening, but without success. I tried

\pdfcompresslevel=0
\pdftrailer{/Encrypt << /Filter /Standard /V 1 /R 2 /P 252 >> }
   Hallo
\end

AFAIK /P 252 allows everything (in revision 2). But you need password 
key sequences /O and /U generation in the /Encrypt dictionary. Even if I 
added them by pdfcrypt utility there was no possibility to comment PDF. 
No idea for now.

Vit Zyka
> 
> 
> Steffen
> 
> 
> 
> Henning Hraban Ramm <hraban@fiee.net> wrote:
> 
> 
>>There's a lot of new or enhanced features for us prepress people, e.g. 
>>for Reader Extensions you don't need this expensive server product any 
>>more, that means, if you own Acrobat 7 Professional you can enable the 
>>correction tools in Reader for your document.
> 
> _______________________________________________
> ntg-context mailing list
> ntg-context@ntg.nl
> http://www.ntg.nl/mailman/listinfo/ntg-context
> 

-- 
Vít Zýka --- http://typokvitek.com
     Automatic document typesetting
     Automaticka sazba dokumentu --
--

Re: ConTeXt tool for enabling comments in PDF ?

[Hans Hagen]

Vit Zyka wrote:
>> Do we have a ConTeXt tool which can enable users of e.g. AdobeReader 7 
>> to add comments to PDF files ?
>> Or is it true that this "comments enabled flag" can only be set for 
>> PDFs generated by Acrobat -- and only by the original author?
> 
> 
> I have played with this yesterday evening, but without success. I tried
> 
> \pdfcompresslevel=0
> \pdftrailer{/Encrypt << /Filter /Standard /V 1 /R 2 /P 252 >> }
>   Hallo
> \end

technically it's possible to have no password (at least the specs say so) but i 
can't get it working;

do you have a file without password that is editable made by another app?

Hans

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                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
      tel: 038 477 53 69 | fax: 038 477 53 74 | www.pragma-ade.com
                                              | www.pragma-pod.nl
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Re: ConTeXt tool for enabling comments in PDF ?

[Vit Zyka]

>> I have played with this yesterday evening, but without success. I tried
>>
>> \pdfcompresslevel=0
>> \pdftrailer{/Encrypt << /Filter /Standard /V 1 /R 2 /P 252 >> }
>>   Hallo
>> \end
> 
> 
> technically it's possible to have no password (at least the specs say 
> so) but i can't get it working;
> 
> do you have a file without password that is editable made by another app?

Unfortunately not. Using pdfcrypt I created encrypted but not editable 
PDF, see http://typokvitek.com/tmp/pdfpermit3.pdf
open password 'A', user password 'B'.

Vit Zyka

Re: ConTeXt tool for enabling comments in PDF ?

[Hans Hagen]

Vit Zyka wrote:
>>> I have played with this yesterday evening, but without success. I tried
>>>
>>> \pdfcompresslevel=0
>>> \pdftrailer{/Encrypt << /Filter /Standard /V 1 /R 2 /P 252 >> }
>>>   Hallo
>>> \end
>>
>> technically it's possible to have no password (at least the specs say 
>> so) but i can't get it working;
>>
>> do you have a file without password that is editable made by another app?
> 
> 
> Unfortunately not. Using pdfcrypt I created encrypted but not editable 
> PDF, see http://typokvitek.com/tmp/pdfpermit3.pdf
> open password 'A', user password 'B'.

it looks like something needs to be done with the stream as well; simply setting 
a password fails (even the empty one, the funny hex stream); btw, your 252 
should be a negative number)

so ... we need more info

Hans

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                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
      tel: 038 477 53 69 | fax: 038 477 53 74 | www.pragma-ade.com
                                              | www.pragma-pod.nl
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Re: ConTeXt tool for enabling comments in PDF ?

[Vit Zyka]

Hans Hagen wrote:
> Vit Zyka wrote:
> 
>>>> I have played with this yesterday evening, but without success. I tried
>>>>
>>>> \pdfcompresslevel=0
>>>> \pdftrailer{/Encrypt << /Filter /Standard /V 1 /R 2 /P 252 >> }
>>>>   Hallo
>>>> \end
>>>
>>>
>>> technically it's possible to have no password (at least the specs say 
>>> so) but i can't get it working;
>>>
>>> do you have a file without password that is editable made by another 
>>> app?
>>
>>
>>
>> Unfortunately not. Using pdfcrypt I created encrypted but not editable 
>> PDF, see http://typokvitek.com/tmp/pdfpermit3.pdf
>> open password 'A', user password 'B'.
> 
> 
> it looks like something needs to be done with the stream as well; simply 
> setting a password fails (even the empty one, the funny hex stream); 
> btw, your 252 should be a negative number)

I see. I have to read the specification notes... But in this case the 
flag number for allowing everything is -4.
(see http://typokvitek.com/tmp/pdfpermit4.pdf)

In this case all Document Security are allowed, but not Document 
Restrictions Summary!? Bu still no success with commenting...

Vit Zyka

Re: ConTeXt tool for enabling comments in PDF ?

[Hans Hagen]

Vit Zyka wrote:

> I see. I have to read the specification notes... But in this case the 
> flag number for allowing everything is -4.
> (see http://typokvitek.com/tmp/pdfpermit4.pdf)
> 
> In this case all Document Security are allowed, but not Document 
> Restrictions Summary!? Bu still no success with commenting...

can you make a file with no password?

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                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
      tel: 038 477 53 69 | fax: 038 477 53 74 | www.pragma-ade.com
                                              | www.pragma-pod.nl
-----------------------------------------------------------------

Re: ConTeXt tool for enabling comments in PDF ?

[Vit Zyka]

> can you make a file with no password?

No. You wrote that this possibility is mentioned somewhere. Where?

VZ

Re: ConTeXt tool for enabling comments in PDF ?

[Hans Hagen]

Vit Zyka wrote:
>> can you make a file with no password?
> 
> 
> No. You wrote that this possibility is mentioned somewhere. Where?

in the pdf specs

\starttext

\startcomment should work in older readers as well \stopcomment \input bryson

\def\pdfnopwdstr{28bf4e5e4e758a4164004e56fffa01082e2e00b6d0683e802f0ca9fe6453697a}

\immediate\pdfobj
   {<< /Filter /Standard
       /V 1
       /R 2
       /P -4
       /O <\pdfnopwdstr>
       /U <\pdfnopwdstr> >>}

\pdftrailer{/Encrypt \the\pdflastobj\space 0 R}

\stoptext

however, it does not work

Hans

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                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
      tel: 038 477 53 69 | fax: 038 477 53 74 | www.pragma-ade.com
                                              | www.pragma-pod.nl
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Re: ConTeXt tool for enabling comments in PDF ?

[Vit Zyka]

>> No. You wrote that this possibility is mentioned somewhere. Where?
> 
> in the pdf specs

Hmmm. I can find only (p. 92 1.6spec):
   "The absence of this entry (/Encrypt) from the trailer dictionary
    means that the document is not encrypted."

It seems to me now that rights without passwords relies with
/Perms in catalog (p.117, 699) and signatures (p.684).
Something like:

-----------------------------
\pdfcompresslevel=0

\immediate\pdfobj
   {<< /Type /Sig
       /Filter % something from Adobe.PPKLite Entrust.PPKEF CICI.SignIt 
VeriSign.PPKVS
       /Contents % signature
       /ByteRange %?? UR3 in /Perms
       /P -4
    >>}
\edef\DocMDPobj{\the\pdflastobj\space 0 R }
\immediate\pdfobj
   {<< /Type /Sig
       /Filter % something from Adobe.PPKLite Entrust.PPKEF CICI.SignIt 
VeriSign.PPKVS
       /Contents % signature
       /ByteRange %?? UR3 in /Perms
       /P -4
    >>}
\edef\URRRobj{\the\pdflastobj\space 0 R }
\pdfcatalog{/Perms << /DocMDP \DocMDPobj /UR3 \URRRobj >> }

Hallo
\end
------------------------------

Sorry for uncomplete code, but I have not studied the signatures yet.
And sorry for a bit out of ConTeXt topic. Hans, is it time to move to 
the pdftex list?

Vit Zyka

Re: ConTeXt tool for enabling comments in PDF ?

[Hans Hagen]

Vit Zyka wrote:

> And sorry for a bit out of ConTeXt topic. Hans, is it time to move to 
> the pdftex list?

no problem, that way users see that things are not always trivial; and ... the 
pdftex list nowadays is mostly a latex howto list

Hans

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                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
      tel: 038 477 53 69 | fax: 038 477 53 74 | www.pragma-ade.com
                                              | www.pragma-pod.nl
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Re: ConTeXt tool for enabling comments in PDF ?

[Hans Hagen]

Vit Zyka wrote:

interesting is that the doc opens but the menu bar freezes -)

\starttext

\startcomment should work in older readers as well \stopcomment \input bryson

\pdfcompresslevel=0

\immediate\pdfobj{<< /Type /Sig /Filter /Identity /P 2 >>} 
\edef\DocMDPobj{\the\pdflastobj\space 0 R }
\immediate\pdfobj{<< /Type /Sig /Filter /Identity /P 2 >>} \edef\URRRobj 
{\the\pdflastobj\space 0 R }

\pdfcatalog{/Perms << /DocMDP \DocMDPobj /UR3 \URRRobj>>}

\stoptext




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                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
      tel: 038 477 53 69 | fax: 038 477 53 74 | www.pragma-ade.com
                                              | www.pragma-pod.nl
-----------------------------------------------------------------

Re: ConTeXt tool for enabling comments in PDF ?

[Vit Zyka]

Hans Hagen wrote:
> Vit Zyka wrote:
> 
> interesting is that the doc opens but the menu bar freezes -)
> 
> \starttext
> 
> \startcomment should work in older readers as well \stopcomment \input 
> bryson
> 
> \pdfcompresslevel=0
> 
> \immediate\pdfobj{<< /Type /Sig /Filter /Identity /P 2 >>} 
> \edef\DocMDPobj{\the\pdflastobj\space 0 R }
> \immediate\pdfobj{<< /Type /Sig /Filter /Identity /P 2 >>} \edef\URRRobj 
> {\the\pdflastobj\space 0 R }
> 
> \pdfcatalog{/Perms << /DocMDP \DocMDPobj /UR3 \URRRobj>>}
> 
> \stoptext

A have had a second look at the Document Permitions. AFAIK and if Adobe 
does not have some bitter secret the situation is as follow:

1) if you want to permit additional document rights available in AR 6,7 
(like commenting, saving, loading  and sending form data) you need to 
sign document. (pgs. 684-700)

2) to sign document you need a) privat/public key generator and b) 
calculate document diggest (number; sum of integers from (nearly) all 
doc dictionary keys and values; alg. p. 1037).

Bellow is the document skeleton for that. There should be:
1) filled the comment lines started by %! (diggest and signature values)
2) perhaps also %? (depends on %!)
3) perhaps the FormSig field is not needed ???

So, to do that, pdfTeX should start to calc document diggest and there 
should be standard(?) process of signing this value.

Vitek Zyka

------------------------------------------------------------------
\pdfoptionpdfminorversion=6
\pdfcompresslevel=0

\def\defObj#1#2{%
   \immediate\pdfobj{#2}%
   \edef#1{\the\pdflastobj\space 0 R }%
}

%--- MDP
\defObj\objTransformParamsMDP{<<
   /Type /TransformParams /P 3 /V /1.2
 >>}

\defObj\objSigRefMDP{<<
   /Type /SigRef /TransformMethod /DocMDP
   /TransformParams \objTransformParamsMDP
%!  /DigestMethod ? /MD5 | /SHA1
%!?  /DigestValue ? ()
%!?  /DigestLocation [? ?]
 >>}

%--- UR
\defObj\objTransformParamsUR{<<
   /Type /TransformParams
   /Document [/FullSave]
   /V /2.2
   /Annots [/Create /Delete /Modify /Copy /Import /Export] % if UR3 also 
/Online /SummaryView
   /Form [/FillIn /Import /Export /SubmitStandalone /SpawnTemplate]
%  /Signature [/Modify]
   /P false
 >>}

\defObj\objSigRefUR{<<
   /Type /SigRef /TransformMethod /DocUR
   /TransformParams \objTransformParamsUR
%!  /DigestMethod ? /MD5 | /SHA1
%!?  /DigestValue ? ()
%!?  /DigestLocation [? ?]
 >>}

%--- Sig
\defObj\objSig{<<
   /Type /Sig
%!  /Filter Adobe.PPKLite | Entrust.PPKEF | CICI.SignIt | VeriSign.PPKVS
%?  /SubFilter adbe.x509.rsa_sha1 | adbe.pkcs7.detached | adbe.pkcs7.sha1
%  /Cert [] | () % only if /SubFilter adbe.x509.rsa_sha1
%  /Contents (?)
   /Reference [
%  	\objSigRefMDP
     \objSigRefUR
   ]
%  /ByteRange [0 0] % should if used UR3 then can be ommited DiggestValue
   /V 1
 >>}

%--- Perms
\defObj\objPerms{<<
   /DocMDP \objSig
   /UR \objSig
%  /UR3 \objSig
 >>}

%--- Sign Form
\defObj\objFormSigField{<<
   /FT /Sig
   /T (SigFieldName)
   /V \objSig
 >>}
\defObj\objForm{<<
  /Fields [\objFormSigField]
 >>}

\pdfcatalog{/AcroForm \objForm /Perms \objPerms}

\starttext
   \startcomment should work in older readers as well \stopcomment
   \input bryson
\stoptext
----------------------------------------------------------------------

Re: ConTeXt tool for enabling comments in PDF ?

[h h extern]

Vit Zyka wrote:

> So, to do that, pdfTeX should start to calc document diggest and there 
> should be standard(?) process of signing this value.

how is that one calculated, imagine that in the %! fields you fill in 
placeholders like hereshouldgosomemagiccode, then one can run a script over the 
pdf, calculate that magic, and replace the string; maybe this can be hooked into 
  xpdflib

Hans

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                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
      tel: 038 477 53 69 | fax: 038 477 53 74 | www.pragma-ade.com
                                              | www.pragma-pod.nl
-----------------------------------------------------------------

Re: ConTeXt tool for enabling comments in PDF ?

[Vit Zyka]

h h extern wrote:
> Vit Zyka wrote:
> 
>> So, to do that, pdfTeX should start to calc document diggest and there 
>> should be standard(?) process of signing this value.
> 
> how is that one calculated, imagine that in the %! fields you fill in 
> placeholders like hereshouldgosomemagiccode, then one can run a script 
> over the pdf, calculate that magic, and replace the string; maybe this 
> can be hooked into  xpdflib
> 
> Hans

Yes, I agree, postprocessing is possible. But I did not find any digest 
computing alg in the range of C/C++ or Perl. Also do not known links to 
xpdflib.

Vit Zyka

Re: ConTeXt tool for enabling comments in PDF ?

[Joachim Schlosser]

> Vit Zyka wrote (long long ago in January):
>> how is that one calculated, imagine that in the %! fields you fill in 
>> placeholders like hereshouldgosomemagiccode, then one can run a script 
>> over the pdf, calculate that magic, and replace the string; maybe this 
>> can be hooked into  xpdflib
> Yes, I agree, postprocessing is possible. But I did not find any digest 
> computing alg in the range of C/C++ or Perl. Also do not known links to 
> xpdflib.
> 
> Vit Zyka

One can sign PDFs with iText (http://itextpdf.sourceforge.net/).
Perhaps this helps a little bit further. I experimented a little bit,
but my knowledge on PDF internas is not yet in a state that allows me
to be quite creative here :-)

Joachim
-- 
Joachim Schlosser
(The e-mail address is fully repliable.)
http://schlosser.info

Re: ConTeXt tool for enabling comments in PDF ?

[Joachim Schlosser]

> Vit Zyka wrote (long long ago in January):
>> how is that one calculated, imagine that in the %! fields you fill in 
>> placeholders like hereshouldgosomemagiccode, then one can run a script 
>> over the pdf, calculate that magic, and replace the string; maybe this 
>> can be hooked into  xpdflib
> Yes, I agree, postprocessing is possible. But I did not find any digest 
> computing alg in the range of C/C++ or Perl. Also do not known links to 
> xpdflib.
> 
> Vit Zyka

One can sign PDFs with iText (http://itextpdf.sourceforge.net/).
Perhaps this helps a little bit further. I experimented a little bit,
but my knowledge on PDF internas is not yet in a state that allows me
to be quite creative here :-)

Joachim
-- 
Joachim Schlosser
(The e-mail address is fully repliable.)
http://schlosser.info