Verify two pfx certificates are not the same without the password
Unfortunately that is hard to do reliably. Depends on how it was stored, See https://security.stackexchange.com/questions/177874/extract-information-about-certificate-from-a-pfx-file-without-the-password?rq=1
If you are unlucky all data is encrypted. In that case you can compare file contents, but binary data can be completely different, even when they contain the same certificate.
Post with information on how to read PFX files