Block.co, a pioneer in Blockchain Credentialing applications, offers an open source platform to issue and verify digital certificates in a completely decentralized way; i.e. with no dependencies to the issuing institution or anyone else other than Bitcoin’s blockchain. This site is a front-end of the open source verification software that anyone can use to validate digital certificates. Certificates are issued as PDF files with special metadata that anchor them into the blockchain.
Please note that the actual PDF of the certificate itself is not published to the blockchain, but rather a fingerprint of the PDF, which is enough to validate that the exact document was indeed published by the issuer and timestamped by Bitcoin’s blockchain.