I need help - I can help - How to lock pdf with digital signature

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How to lock pdf with digital signature

Printed From: Debenu Quick PDF Library - PDF SDK Community Forum
Category: For Users of the Library
Forum Name: I need help - I can help
Forum Description: Problems and solutions while programming with the Debenu Quick PDF Library and Debenu PDF Viewer SDK
URL: http://www.quickpdf.org/forum/forum_posts.asp?TID=3914
Printed Date: 28 Apr 24 at 11:51AM
Software Version: Web Wiz Forums 11.01 - http://www.webwizforums.com

Topic: How to lock pdf with digital signature

Posted By: mimkawee
Subject: How to lock pdf with digital signature
Date Posted: 10 May 21 at 10:02AM

Hello.

We are implementing embedded digital signatures in PDF files. One of the requirements is to be able to provide a locking functionality, preferably after a signature has been placed.

What we found so far is to use the Encrypt function to prevent any changes to the file but when there is a signature in the file it is no longer valid after encrypting.

The other thing that we tried is to encrypt the file first and add the signatures later. That works on Windows 10 but on Windows 7 the file requires a password to be provided. The Encrypt function is being called with an empty string for parameter user password.

Is there any other way to lock the pdf file or a fix for Windows 7?

*Edit *

After further testing was discovered that the OS is not the factor in the password problem, but the version of the pdf file. The problematic version is 1.4.

I have tried to change the version to 1.5 (since files with that version do not preset the problem) but even after that password is required.

Thanks.

Replies:

Posted By: Ingo
Date Posted: 10 May 21 at 9:14PM

Hi Mariya,

from my understanding signing is the last process on a pdf.
It's almost like a seal.
You can't change it the other way round.
This is what's Google telling:
The digital signature and the PDF document are linked cryptographically and given a tamper-proof seal. Clearly. The personal data and the identity of the signatory are legitimized using a unique digital certificate and a PIN.
This means to you entering an encryption afterwards will broke the signature/the seal.

Cheers and welcome here,
Ingo

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Cheers,
Ingo

Posted By: mLipok
Date Posted: 17 May 21 at 3:32PM

There is no need to lock pdf.
There is a need to check if was or not modified.

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Here you can find description how to test my examples:
http://www.quickpdf.org/forum/forum_posts.asp?TID=2932&PID=12600&title=drawcapturedpagematrix-matrix-howto#12600