Thanks for the replies, guys.
I extracted OBD mission folder to desktop (just an old habit I formed with CFS2-I intended to keep it there for ease of use, thinking the original would stay in place). Moved PD's stuff into that folder. When trying to start game and use missions, I got an error message that I needed to reinstall CFS3 disk 1 and BHAH complete. (I did place OBD mission folder back where it belonged prior to trying new PD missions (so I thought).
I have only had the game for a few days and haven't tried Campaigns yet. Excited to do so. I'm no whiz with a puter and do not intend to be. PD was a huge help to me when OFF first started and sent me lots of disks and advice. I've since moved up to broadband from dial-up. Good to know Phase 3 stuff will work with BHAH.
Started all this with Red Baron 2 and CFS1 many years ago. Recently decided there is room in retirement for flight sims again. WWI has special appeal. May even look at multi-play after I practice a bit.
I'll make another attempt to get me some more missions later. Thanks!