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Certificate for signing a pdf file
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Posted by jeremie  · 16-10-2020 - 14:59

I'm trying to sign a PDF file.

I bought a certificate from GlobalSign. They sent me a .pfx file that I converted to a .pem file. Then I signed the PDF using your code:

require_once $root.'Libraries/phpdocx-premium-9.5/classes/SignPDF.php'; 
$sign = new SignPDF(); 
$sign->setPrivateKey('Test.pem', 'phpdocx_pass'); 

'Test_signed.pdf' is created and I can see the signature in it when I open it with Adobe Acrobat Reader.

I can see my name on it, but Adobe displays a message saying that the validity of the certification is uknown because they can't authenticate me.

What am I missing?


Posted by admin  · 16-10-2020 - 15:48


Adobe, and other programs, displays the validity of the certification is uknown message when the certificate/CA is not trusted by Adobe, so you need to accept (trust) it or use a certificate accepted in Adobe as trusted.

We recommend you to check if AATL is updated in your Adobe PDF reader ( and the certificate/CA you are using is trusted by Adobe. 

On you can read more information when Adobe displays that message.