Do you happen to have any plugins that you think might prevent linking a file from another website or anything? I would try deactivating some plugins and seeing if it works after that.
Do you have an error log or anything with your hosting that could tell you more?
The other thing you could try is going right into the HTML editor and putting this in and seeing if it works:
<object type="application/pdf" data="https://porttownsendrotary.org/Jumping-Mouse-Story.pdf" width="100%" height="600"></object>
That is what code my plugin should generate anyway so you could try to put that directly into the HTML editor and see if you can see anything. If you can’t see anything by putting that directly in it may be your hosting setup that is causing the issue.