Office 365 SharePoint and PDF files…
Recently, O365 added some server side rendering of PDF files. Problem is if you have PDF files and an anonymous site, if a user clicks the PDF link, it will then try to authenticate that users. Which defeats the purpose of anonymous.
You’ll need to change the links as follows:
Append either to the following (1st opens in the server side PDF reader; 2nd downloads to the client to read.
to the end of the URL.