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I've used various methods (mentioned elsewhere on this site) to create PDFs, using a printer driver or converting from PostScript, etc. The common problem is that if I open any of the output files in the newer versions of Adobe Reader, there's an option to "Place Signature" but it's greyed out, or gives an error message that the feature has been disabled for this document. As far as I can tell, there's an option set somewhere in the document metadata that tells Reader "allow the user to sign this document", or don't. None of the free/open source tools that have been been linked to in other SU posts have had this listed as an option (though to be fair I haven't actually downloaded and tried all of them).

Is there a tool that does this? Can I just poke a bit with a hex editor somewhere to turn on this functionality? I can sometimes get access to Acrobat Professional to turn on this option, but doing it for every desired case would be more work than I care to do. The current workaround for single-page documents is:

  1. Print the document to PDF (possibly via postscript)
  2. Open a single-page blank PDF with the "signable" bit turned on in Reader
  3. create a custom "stamp" using the Reader markup tools, by importing the printed-to document
  4. "stamp" an image of the printed document on the blank page, hoping to get it centered about right
  5. place a signature over the document-but-not-really you just stamped

This obviously does not scale well at all. It would be much better if I could:

  1. Print the document to PDF
  2. Drag the document to a simple shortcut / tool / whatever
  3. Open the document in Reader
  4. Place a signature in the document

ETA: Sorry, maybe I should have been clearer -- I'm talking about the certificate-based digital signing available in Adobe Reader, not adding a virtual ink signature. Also, any solution really would have to be available offline.

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4 Answers

up vote 3 down vote accepted

After coming across this post, I found a free software called Digisigner which has the sole function of signing existing PDFs, whether Reader allows them or not. After that, Reader shows and validates the signature 100%. It's a workaround, but not nearly as complex as yours. It allows both the invisible signatures and visible stamps. There are some catches:

  • its renderer being unable to show ligatures, but once signed and reopened it's exactly as it was)
  • the big downside for me is that it can't use public-key encryption or set the "signable" bit so that Reader will sign it.
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I have no idea how they get away with it (contrary to the spec citation above...) but I'm not going to look a gift horse in the mouth. This is pretty sweet! –  Coderer Jan 7 '11 at 23:55
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Well, this passage from the PDF 1.7 spec doesn't look too encouraging:

12.8.2.3 UR

The UR transform method shall be used to detect changes to a document that shall invalidate a usage rightssignature, which is referred to from the UR3 entry in the permissions dictionary (see 12.8.4, “Permissions”). Usage rights signatures shall be used to enable additional interactive features that may not available by default in a conforming reader. The signature shall be used to validate that the permissions have been granted by a bonafide granting authority. The transform parameters dictionary (see Table 255) specifies the additional rights that shall be enabled if the signature is valid. If the signature is invalid because the document has been modified in a way that is not permitted or the identity of the signer is not granted the extended permissions, additional rights shall not be granted.

EXAMPLE

Adobe Systems grants permissions to enable additional features in Adobe Reader, using public-key cryptography. It uses certificate authorities to issue public key certificates to document creators with which it has entered into a business relationship. Adobe Reader verifies that the rights-enabling signature uses a certificate from an Adobe-authorized certificate authority. Other conforming readers are free to use this same mechanism for their own purposes.

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So long story short, it sounds like the only way to say "hey Reader, let this document be signed" is to do it from an application "with which [adobe] has entered into a business relationship"? Wow, that's... that's terrible. Not surprising, given the overall crap-ness of Adobe generally, but still terrible. –  Coderer Apr 5 '10 at 19:40
    
@Coderer: actually, I think it's not so much that you have to use an Adobe app as that you have to obtain a certificate specifically for this from one of the CA's they've authorized for the purpose. –  SamB Apr 7 '10 at 22:48
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I've had some success with tools from the following vendor, from a quick Google of their site it seems that their free viewer at least supports signing, it may be possible that their PDF creation software would satisfy your requirements:

Docu Track

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From their web site, under "Advanced/PRO features" (e.g. for-pay): * Add Digital Signatures (incl. Time Stamps) Besides, the free Adobe Reader can sign, the only value in a 3rd-party reader app would be if it ignores the "allow / block signing" permission set in the file. –  Coderer Mar 15 '10 at 21:47
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Check out https://www.fillanypdf.com/ will allow you to fill and sign pdfs online.

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The OP has specifically asked for an offline solution. –  Dan Dascalescu Sep 24 '11 at 10:59
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