It appears that the Windows installer is failing to remove file associations from the registry. I discovered this when trying to use the editor as a stand-alone program, having (some years ago) uninstalled Calibre64 and replaced it with Calibre32 (
https://www.mobileread.com/forums/sh...d.php?t=289481) -- there were some 74 file associations under HKCU\Software\Classes (calibre64.AssocFile.*, calibre64Editor.AssocFile.* and calibre64Viewer.AssocFile.*) which had not been removed, and which prevented me opening the editor from the "open with" menu.