I made a bunch of markups to a document in preview, went to save and it converted the multipage doc to a single page document (losing the other 12 pages of markups). I've tested saving multiple different ways. Does preview not have the ability to save markups to a multipage document?
iMac 21.5″, macOS 11.6
Welcome!
See if this helps:
Combine PDFs in Preview on Mac - Apple Support
It's possible to extract a single page of a multi-page pdf by dragging that page's thumbnail to the desktop. You can edit or mark up and then return it to the original using the "Combine..." article, or create a new pdf with your markups by opening a new file and dragging all the singles to its thumbnail sidebar in the order you want.
The page I linked is but a part of a nice overview and tutorial for Preview. Note the Table of Contents link near the top.
Thanks Alan. Unfortunately, that doesn't help. I'm trying to markup and save a document that is already multiple pages. In preview, when I save the document, it removes all but the first page.
Saving multi-page PDF in preview without losing pages
