Have used this plugin with success in the past, so this may be a matter of "new WordPress, old plugin."
The problem: after plugin installation (with refresh and reset of permalinks) I get an error on uploading the file. It uploads it fine, but it throws back and error message saying there was a problem and does not include it in the list. When I try to point it to a remote file (that is, to this file but with its full name) it also does not work.
I opened the file myself, so it's working (and after giving up on this, I now have it displayed via the Embed PDF plugin). Merely posting this for the developer and those who may encounter the same problem.