PDFs won't save after I extract pages

When I extract pages from .pdfs, it won't let me save the new one with fewer pages. If I close out of it, it reverts to what the original .pdf was before I extracted any pages.  I have unchecked the Enable Protected Mode and Enable Enhanced Security boxes under Security (Enhanced), but they will won't save after I extract pages. If it helps, these are large .pdfs that I downloaded from Logikcull that I then have to split into parts of 400 pages or less so that it doesn't crash Adobe. Please help. I have discovery due!!