Hi all following this thread!
The bug preventing you from dragging external files onto Axure RP’s canvas was an issue specific to Windows and has been fixed in a release candidate of Axure RP 9 (9.0.0.3659).
If you’d like to try out that build, open up Axure RP 9 then go to Help > Check for Updates and check off the box for “Include beta channel builds”. Alternatively, check out our Axure RP 9.0 Beta Channel (Release Candidate) Updates post.