Thanks a mil for the tips, GeoffC and kacir, I'll try them out.
Just did -- the rtf conversion in Calibre went fine, didn't have to tweak anything. Hurray! Won't try Aspose after all because it requires .NET, which I've had on my laptop twice and deleted it twice because it was slowing everything down a lot.
After all this, I just learned about PB
901. I wonder if it will handle PDFs better.