Giant file can't save, can't delete pages

I purchased a clip art bundle from a graphic designer, who despite being a gifted artist, doesn't seem to understand the tech side of it.  Rather than send individual images I can open as needed, she sent one giant 17,000 page .pdf.  I can open it, but it's too big to save on my computer.  I don't necessarily need the whole thing though.  I would like to delete the pages I don't need (probably at least 75% of them, if not more).  It would make the file size small enough to save and quicker to search through.  Unfortunately, Acrobat won't let me delete pages.  I keep getting a "one or more pages could not be deleted" error message.  I've tried deleting multiple ways, no go.  I've also tried extracting just the pages I need.  I get an error message with that as well.  I've reached out to the designer and she doesn't seem to understand my problem.  She did reluctantly agree to refund my money, but it seems like there should be some way to make this work.  Is there a way to delete pages, extract useful pages, break up the file, or optimize it without saving it?