problems with signature fields

[Pablo Rodriguez <oinos@gmx.es>]

Hans,

I have the following sample:

  \setupinteraction[state=start]

  \starttext
  \startTEXpage[offset=1em]
       \definefield[x][signature]
       \field[x]
  \stopTEXpage
  \stoptext

I can only use Acrobat to sign PDF documents with signature fields
generated by ConTeXt. Other tools sign the PDF document not producing a
valid signature (Acrobat cannot read or validate it).

From the source, signature has two objects (copied from the sample above):

  2 0 obj
  <<
    /DA (/rmtf 11.9552 Tf 1.1955 Ts 0 0 0 rg 0 0 0 RG)
    /DV <FEFF>
    /F 4
    /FT /Sig
    /Ff 0
    /Kids 1 0 R
    /MaxLen 1024
    /Q 0
    /Subtype /Widget
    /T <FEFF0078>
    /V <FEFF>
  >>
  endobj

  4 0 obj
  <<
    /Type /Annot
    /DA (/rmtf 11.9552 Tf 1.1955 Ts 0 0 0 rg 0 0 0 RG)
    /F 4
    /Parent 2 0 R
    /Q 0
    /Subtype /Widget
    /Rect [ 14.033054 14.033054 70.40415 25.08072 ]
  >>
  endobj

One of the tools that has issues with two objects for the signature
field is the latest version (1.18) from mupdf-gl.

mupdf-gl adds the signature value to the child (object 4) and not to its
parent (object 2).

I’m afraid this is also the same issue that AutoFirma (a e-signing tool
developed by the Spanish government
[https://firmaelectronica.gob.es/Home/Descargas.html]) has with these
signature fields.

When both objects are merged in one (as Acrobat Reader does when saving
a copy), both tools generate documents contaning signatures totally
unproblematic to be read validated by Acrobat.

I suggested merging both objects back in 2017. You told me that
simplifyng this would introduce too much complexity in ConTeXt only to
save some bytes.

Back then, I thought it was an minor improvement. Now I realized that
this two objects for signature fiels are only valid for Acrobat.

I wonder whether this improvement might be also easier to make in LMTX.

Would it be possible that signature fields may have only one object, so
that mupdf-gl and other tools have no problem signing fields PDF
documents generated by ConTeXt?

Many thanks for your help,

Pablo
--
http://www.ousia.tk
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