can i sign pdf file with an existing pfx file

we have created a solution using Adobe Signatures that works fine on the desktop applications. We register a pfx signature file when they sign up and store it on our system. Then when they want to apply for a new permit, they sign with the same signature that was registered. Then we check the signatures to verify their identity.

Is there any way to sign with a pfx file from a mobile device? The only thing I have found is using typed or touch screen signed signatures on mobile devices. This is not acceptable because we can not verify who signed the document.

Thanks in advance for any advice or comments.

Michael