Who can tell me why PDF files exported from CAD / revit are slow

I have had continual problems with this too.  I had a large CAD file map from an architect.  It was large but it had worked fine.  Then all of a sudden, it didn't.  It was the weirdest thing.  I had created room numbers and icons all over the map, a map key and just had a few more edits.  I sent it for review.  When I opened it the next time, it took 20 minutes in between each keystroke and I couldn't see where I was moving objects.  I just had to wait for it to 're-draw'.  I almost couldn't finish my project.  Adobe's answer to my problem was much that of another responder, "make the map into imported art and draw on top of it."  But you loose all editing capablities of the file.  Then last minute they tell you they added a wall or moved a door.  I was working on a school that was 3 levels the size of college campus, with 3000 rooms the building was circles.  This was not something I wanted to REDRAW it would have taken weeks.  I don't have an answer, I'm qualifying that this is A PROBLEM and I feel like they recently updated the program and made it worse for this somehow.  It handles LESS DATA than before.