Older versions of PGP were designed for Windows XP or Vista. They often crash or fail to encrypt properly on Windows 10 or 11.
A legitimate user would receive a license number (the "serial key") upon purchase, typically in an email confirmation with an attached PDF file. This license number had to be entered during installation and then authorized with PGP Corporation's (later Symantec's) activation servers, either automatically or manually. PGP Desktop Professional v9.7.0 Serial Key
: Available on Windows Pro and Enterprise editions for full disk encryption. Older versions of PGP were designed for Windows XP or Vista