Press F1 while VoiceAttack has focus to open VoiceAttackHelp.pdf in your default PDF viewer.
That is possible, yes.
If you are familiar with .NET (I would personally recommend C#, though VB.NET can also be used) you can write inline functions (that can either be compiled on-the-fly, or to a .dll and then called), or plugins (which must be precompiled to a .dll and called using the "Execute an External Plugin Function" action).
The "VoiceAttack Plugins (for the truly mad)" section of the documentation describes these features.
Users also share their
plugins and
inline functions on this forum, and others can be found using a search engine.