Verify that a signed PDF file is generated from a specific PDF file

[Ale123]

Hi,
I am using iTEXT libraries.
I need to verify that a signed PDF file is generated from a specific PDF
file.
I try to better describe the scenario:
I have a PDF file called PDF1. I affix to it the signature, so I obtain a
signed PDF file, that we call PDFs.
I need to find a way to verify that the PDFs file is generated from PDF1
file: if PDF1 has been modified in PDF2 before the signature, I need to be
able to understand that the file has been modified and that the PDFs file
hasn't been generated from PDF1.
Is it possible to verify it?

thanks!
alessandro