sure, you have to pass absolute path of p12 or pfx file as certfile.
if you still sign field as wrong, please share your pdf file before signed, and pdf file after signed.
also, please attach your test cert file, that make wrong sign data.
we will check it.
Just to give you more info. I just signed the same document with PDFBox, using the same p12 file.
It has some info printed into the signature, but that it is just for visual effect.
But as you can see, if you accept the certification, Acrobat Reader does approve all 4 signatures.
I'm sending the pdf file for comparison