Say I'm searching for the keyword "apple" in a PDF document using Microsoft Edge. The search immediately starts as I type in the first letter of the keyword, in this case "a". Edge then struggles to find all the numerous instances of this letter, which takes it about 10 seconds, during which Edge is not responding. This makes searching PDFs using Edge very tedious, rendering Edge irrelevant for PDF viewing and editing.
The PDF search issues are deeper than that. I cannot reliably open and search a PDF in SPO. Reliable Search is sporadic at best and usually so unreliable that I have to download a PDF to my desktop and work from there.