Welcome @Servinjesus1
This has already been reported multiple times on the forums.
https://discourse.devontechnologies.com/search?q=pdf%20issue%20order%3Alatest
That being said…
Is there a crossed-pencil icon on the right of the Navigation bar above the view.edit pane? If so, the property icon shows it is read-only, most commonly due to fonts that aren’t compatible with Apple’s PDFKit. In such cases, annotating a problematic PDF like that can lead to the entire text layer being corrupted. Therefore, DEVONthink detects it as a potential problem and sets it to read-only for safety.
With problematic documents, I would suggest trying Data > Convert > To PDF (Paginated) first. If that doesn’t work, you can open the document in an external PDF application like Preview, and annotate there.
Development also suggests this: Select the Help > DEVONthink 3 Help > Documentation > Appendix > Hidden Preferences. On macOS Monterey or later, Control-click the On link for ForceEditablePDFs. Then paste the URL into the address bar in Safari, okaying opening DEVONthink. This should minimize false positives when detecting potentially problematic documents.