Returns or sets the ProductFamily string for the application identity.
The max length is 32.
All the application identity information should be set prior to invoking
OpenSourceManager(). Since with built-in Wizard Mode, Dynamic TWAIN manages the transition of TWAIN state intelligently,
OpensourceManager() may be called automatically by other TWAIN related functions, such as
AcquireImage(). It is recommended that application identity information be set prior to any other TWAIN functions.