Feature Request: Support for `/Prop_Build` in PDF Signature Dictionary (PAdES)

[nobrother]

Feature Request: Support for /Prop_Build in PDF Signature Dictionary (PAdES)

Summary

Currently, @libpdf/core does not expose any way to set the PDF signature build properties (/Prop_Build) inside the /Sig dictionary.

As a result, PDF viewers such as Adobe Acrobat display:

“Signature was created using: Not available”

even when:

• AATL trusted certificates are used
• TSA timestamps are included
• PAdES signatures are valid (ETSI.CAdES.detached)

---

Problem

In the current implementation of PDFSignature.sign():

• Signature dictionary supports:
  • Reason
  • Location
  • ContactInfo
  • SubFilter
  • ByteRange
  • Contents

However, it does not include /Prop_Build, which is used by Adobe Acrobat and other PDF viewers to display the signing application identity.

Possible fix:

const signatureDict = PdfDict.of({
  Type: PdfName.of("Sig"),
  Filter: PdfName.of("Adobe.PPKLite"),
  SubFilter: PdfName.of(resolved.subFilter),

  Prop_Build: PdfDict.of({
    App: PdfDict.of({
      Name: PdfString.fromString("Documenso"),
      R: PdfString.fromString("1.0")
    })
  }),

  ByteRange: createByteRangePlaceholderObject(),
  Contents: createContentsPlaceholderObject(resolved.estimatedSize)
});