Signinig a signed PDF preserving the validity of the original signature

Posted by: Zabelin_g on 13 June 2018, 6:51 pm EST

  • Posted 13 June 2018, 6:51 pm EST

    I downloaded example solution from this path
    “ Signinig a signed PDF preserving the validity of the original signature”
    and after starting with standard values, I received a file signed twice, but one of the signatures is not valid

    (attached file)

    we plan to acquire a license
    “Documents for PDF Unlimited”
    but are not sure that the functionality we need works

    Can you help us?
    Thank you
  • Replied 13 June 2018, 6:54 pm EST

  • Replied 13 June 2018, 6:56 pm EST
  • Replied 14 June 2018, 8:57 pm EST


    Thank you for bringing this to our notice. We are in discussion with the development team [Internal Tracking ID:327555] over the same and will get back to you as soon as it is done.

  • Marked as Answer

    Replied 15 June 2018, 1:03 am EST


    Thanks for bringing this to our attention. This is not a bug (read on) but I probably need to add an explanation to the sample itself.

    The problem occurs when you run the sample locally because GcPdf then runs unlicensed, and adds the red nag page caption to the generated PDF. So this (correctly) invalidates the first signature. On the web sample server, we run a licensed copy and all works as expected. So if you get a license, the local sample will also work correctly.

    Hope this clarifies the situation. I will now mark this thread as 'answered' but please let me know if you have further questions.

  • Replied 16 June 2018, 7:14 pm EST

    thanks for your reply

    When I use the license code received from you by mail, I still have the same error.
    what function am I verifying the validity of the license?
    In addition, there is another question:

    if I use the example code from your site in the console application (.net 4.6.1) - it works fine (sign pdf)
    but since I have to open the interface for visual basic 6 - I use these functions in the class library - for testing calling functions from console application with reference to class library I get various errors about missing components (although all the necessary reference to dlls are created) - is this a known problem?


  • Replied 18 June 2018, 7:01 am EST

    Re your 1st (original) question - the SignIncremental sample creates two instances of GcPdfDocument (doc & doc2). From your screenshot I'm guessing you only licensed the first instance. To license all instances, call the static GcPdfDocument.SetLicenseKey() method before you create the first GcPdfDocument (you can then omit the key from the ctor calls). Let me know whether this helps.

    As for your 2nd question - I am not sure what the problem is, it sounds as it could be related to how VB works with .NET Standard and not GC-specific. But I cannot be sure without more info or an actual sample. If you want you can email me your project (dmitry.yaitskov at and I will see what's going on.

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