Edit: Yes, Synapse is Windows 10 compatible. I had some initial issues after a corrupt Windows 10 install. =-=-=-=-=-=-=-== I am getting some nasty fatal synapse errors on a new Windows 10 PC. It's either a Rebol compatibility or a ghostscript error. In results clicking [Original] results in a fatal error. @Graham - have you tried Windows 10 ? 8 works fine. The .pdf document you are trying to view appears to download, but it crashes when it tries to display it.