Can't delete a page. Get "bad parameter" error. Can re-pdf but lose all bookmarks that way.

I have 9.5.3 pro extended, with Win 7. These are saved-as-pdf-from WORD files that I foolishly saved with defaults to include whatever data MS throws in there.

I've learned not to do that, but still have quite a number of long, book-length documents that I occasionally need to edit. I can add new (corrected) pages but

not delete old ones.

I ran the "Repair Acrobat Installation" from the Help pull-down.

I tried the "PDF Optimizer" function from the "Advanced" menu, to discard user data and all objects except bookmarks and thumbnails, but I got a conversion error.