PKI signature scheme with CAs issuing digital certificates has been in operation for many years. It works, albeit not without issues. There have been several occasions that CAs have been hacked (and in some cases it was even an inside job) so that certificates, and thus all security depending on them, were compromised. I.e. CAs are a central point of failure. vPDFs provide a practical way to ensure that several public online sources are consulted to ensure identification of an entity’s public key thus improving on the centralized nature of CAs. The actual data and signatures are also immutable and tamperproof further improving on trustworthiness.
In addition, the PDF signature mechanism makes use of a feature called Incremental Updates to add signatures which was proved to be prone to several attacks, effectively bypassing the signature. VPDFs use the simpler and more practical solution of hashing the entire document, therefore eliminating this type of attacks.