400 PAGES!!!!!
This is way too big for a single PM doc. Better to aim for a number of smaller files of around 20 pages each, and when complete, you can 'book' and print them as one, or convert each smaller file to PDF and combine them into one PDF using Acrobat.
If you can open but not view the current large document, then make save several copies - at least 10 to start with - with different names. Then open each copy, and using the Layout menu, delete all but the first 20 pages from the copy and save and close. Open the new file and see if it appears as normal before continuing the process, which will be time-consuming, but worth it if it works.
Keep deleting pages from all the copies - leaving 20 pages at a time - of course, a different set of pages each time.