PDF is uneditable after importing

When I import a PDF from the web, sometimes, I am unable to edit (highlight) the content of the PDF unless I open it in an external editor first like Preview and then make a change there and resave the document.

What is happening in DevonThink that prevents me from doing the initial edits in place? Is there something I need to do in DT?

See release notes of version 3.8.1:

And as an addendum to the above comments, this does not mitigate the potential issues that were detected. It’s not a fix for incompatibilities with PDFKit; it just allows you to “give it a shot” instead of inhibiting someone’s efforts.