Possible solution to "damaged" PDF in Apple Books that would no longer open!

Hello everyone! Unfortunately, yesterday evening, I encountered a problem with the Apple's Books app on my iPad in which when I was trying to access the PDF of my medical textbook, I could no longer open that file and was instead given an error message that stated "It may be damaged or use a file that Preview doesn't recognize." After seeing a previous discussion post on the Apple Community forum and Reddit for this same type of issue, I was beginning to think that the hours and hours of annotating I had done on that file would be lost.

However, after multiple attempts trying several different routes, thankfully the PDF was recovered with my notes intact! As such, I am making this post to explain the solution that worked for me and to encourage anyone encountering a similar problem to not lose hope.

Here's what worked for me...

1. On the iPad Books app, there should be three dots at the bottom right of the given PDF you are trying to view. After clicking that, I then clicked "Share PDF" followed by "Save to Files", in which that file was then located in my iCloud Files drive (accessible via Finder on my Mac)
2. On my Mac, I then downloaded Adobe Acrobat (at the time of this post, there was a free trial available)
3. On Adobe Acrobat, at the top left I clicked "Create" --> "Create a PDF" --> "Select a file" (within Single File tab) --> selected the saved PDF (from above) that Books told me was "damaged" --> "Open" --> "Create". After that, the PDF appeared intact and fully operational within Acrobat.
4. Then, to save this to my computer, I selected "File" --> "Save As" --> selected the appropriate location within Finder.

Although this thankfully worked for me, I'm not sure how reproducible the results are, but nonetheless I wanted to share this in the hopes that it does work for others and save them time and emotional energy – since I know how tough it was when I thought I lost my work. Wishing everyone a Happy New Year!