Thanks for getting back
"Do you get invalid
signed/certified document when you do multiple text signatures and then do
"text" style signatures, then a "digital" style signature
works without any errors. However, the "text" style
signatures do not involve a digital certificate, so do not track or verify the
document at the point that the user "signed" it.
We have been playing
with the manual signing features in Adobe Reader XI - if you use the
"Fill & Sign" sidebar, then the "Work with
Certificates" section, it shows the options for "Certify" and
also "Sign with Certificate". We dug a bit further into PDF
digital signatures, and found this reference: From: https://www.adobe.com/devnet-docs/acrobatetk/tools/DigSig/Acrobat_DigitalSignatures_in_PDF.pdf
PDF defines two types of
signatures: approval and certification. Both types are byte range signatures
over all file contents. Both take a visual snapshot of the document at the time
it was signed and thus provide a high level of document integrity.
The differences are as
- Approval: There can be
any number of approval signatures in a document.
- Certification: There
can be only one certification signature and it must be the first one in a
It appears that
the GroupDocs "digital" style signature is the
"Certification" type, and it sounds like what we're after is the
"Approval" type - and ideally both. That way we could
certify the document, then place Approval signatures for potentially several
Unfortunately it appears
that there's no capacity for GroupDocs to add "Approval" fields at
the moment, unless we missed something?