Convert PNG to PDF and apply signatures using Aspose.PDF for .NET - Signatures are invalid

Hi Aspose Team,

We are converting a transparent image PNG to PDF using Aspose Pdf for .NET 17.9. Once the document is converted we are applying certify signature (via all three possible permissions according to ISO 32000-1:2018) on the converted PDF document. Once certify signature is applied, Adobe Reader or Acrobat Pro shows signature INVALID.

Would you share what’s wrong with it resulting certify signature INVALID? I have attached both signed and unsigned PDF documents in the thread?

Your quick feedback on this is appreciable.

SH-Logo-unsigned.pdf (38.6 KB)
SH-Logo-signed.pdf (619.8 KB)

Kind Regards,
Israr Ahmed


Thank you for contacting support.

Would you please share SSCCE code so that we may try to reproduce and investigate it in our environment. Before sharing requested data, please ensure using Aspose.PDF for .NET 19.6.

Hi @Farhan.Raza
I have further invested the issue with the latest Aspose.Total version 19.11.
Let me explain the issue step wise:
1: I have converted the PNG image to PDF (PDF_A_2A) using the attached document conversion utility:

2: Open the converted file in Adobe Acrobat XI Pro.
3: Edit the document as a form to add signature field or any field in the document and following error is displayed by Adobe:
image.png (22.7 KB)

4: If bypass the Adobe warning and continue adding signature field and sign the document, the document remains valid after applying signature but if same scenario is performed on the converted document and signature field is added in the converted document using iTextsharp and sign the document, the signature becomes invalid. (Document attached)
Signed document - Invalid.pdf (209.3 KB)

PN: The same error is displayed by ADOBE in another reported issue for .DOCX document in another scenario.

There is some major issue in your document conversion. Please help us out in this regard.


Can you please share complete working sample project to reproduce issue so that we may further investigate to help you out.

Hi @Adnan.Ahmad
I have shared the document conversion utility in the above comment. Basically the issue is when convert the attached PNG image to PDF and edit the converted PDF as a form in Adobe Acrobat, Adobe displays an error regarding document structure.
This only require a document conversion utility which is already provided in the above comment and only needs to place a license file in License folder.


I have worked with sample project shared by you using Aspose.PDF 20.1 and unable to observe the issue. I have also shared my generated result for your kind reference. Can you please try to use latest versions of both API’s and share feedback with us.11convertedFile.pdf (44.0 KB)

Hi @Adnan.Ahmad
I have downloaded the converted file provided by you and edit that document in Adobe Acrobat XI Pro and same issue has been observed. Please see the attached image:
image.png (46.7 KB)


Thanks for providing requested information.

An investigation ticket as PDFNET-47575 has been logged in our issue tracking system for further investigation on this scenario. We will further look into details of the issue and keep you posted with the status of ticket resolution. Please be patient and spare us little time.

We are sorry for the inconvenience.