I have a project, which needs to verify a doc or pdf file whatever it has a digital signature or not.If the file has a digital signature, then is it valid or not?

I know, it may be possible in java, but I need to do it in php.

OpenSSL is used to encrypt and decrypt, but do not know how to check doc/pdf with it.

Please help this newbie, any feedback will be a big help for me.
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