Sorry for late reply.
If I do drag and drop, I get an Acrobat error & a javascript error.
If I use the canonical uri method (which I'd prefer), I get the same Acrobat error, but no javascript error.
Acrobat is not the default pdf reader on my system (OSX).
Thinking it must be the Acrobat NPAPI plugin, I removed AdobePDFViewerNPAPI.plugin & AdobePDFViewer.plugin from /Library/Internet Plug-ins/ , but Acrobat error persists in TW Desktop
So I'm still stuck