I uploaded all my pdf files to the WordPress Media Library and copied all the links to them. Then on a page, I just put a link to that pdf file.
BUT most if not all, show the blocking Microsoft Defender SmartScreen. What used to be a popular section of my website has dramatically dropped in visitors!
I have filled in Microsoft’s form: “Report that this site doesn’t contain phishing threats” and had to put all the pdf addresses in that were displaying the red screen of death, but I am not holding my breath!
So I do not believe that this is a plugin problem.
Also, many website owners may not realise this is going on.