DigiSigner is a tiny PDF viewer tool to digitally sign PDF documents and verify signatures. DigiSigner supports certificates from your Windows key store, smartcards (PKCS#11) and file key stores (PFX/PKCS#12). DigiSigner shows and verifies existing digital signature in the document. You can use right-click mouse menu to quickly open PDFs in DigiSigner. There are versions for Mac and Linux.