It's hard to tell from this post exactly what happened to you. Your printer software experienced some registry corruption, and you think Foxit PDF reader is to blame? More to the point, you think Foxit intentionally
introduced some bad agent into your system whose purpose was to cause this registry corruption?
I'd be interested to find out how you came to this conclusion. Registry corruption occurs all the time and for a variety of reasons. Generally there's no way to tell how it happened, so if you've found a way to audit registry changes and trace them to individual programs, that would be news in itself!
If you think the damage was caused by a corrupt PDF opened in Foxit, I'd say that's more an issue of where you are getting your PDFs from than a Foxit problem. No software - commercial or open source - is immune to security holes. That's why Adobe and MS release so many patches, and release them so regularly. OSS does the same. The issue is more about keeping current on your applications and using common sense about downloading and opening files.
In some sense (theoretically) OSS should be more secure, because when security holes in OSS are found, they can be patched and released as quickly as the community finds out about them. Exploits in commercial software have to be reported, then the fix may wait for the marketing team and the legal team to weigh in, then it will be scoped into the development schedule and at some point - only if it's economically justifiable, of course - a patch might be issued. Or the decision might be made to roll the fix into the next scheduled release, still X months away and costing Y dollars for the upgrade.
But still - without knowing more it's hard to tell if your conclusions are correct: that this was a deliberate attack on your system, and that Foxit was really the vector for the attack.
P.S. - Printer vendors are not generally known for the high quality of their software. In my experience, printer software ranges from moderately OK to unbelievably awful. It's typically buggy, intrusive, and rude. Another reason I'd like to know more about the incident.