To launch conversions via drag & drop, context menu, command line or HotFolder PDFCreator requires to automatically print the requested file. Therefore PDFCreator will look up the associated command to print the file type in the Windows registry. If there is no print command registered for this type of file, or if the command is registered incorrectly, the file can’t be send via printing to the PDFCreator printer to convert it.
It is often possible to solve this issue by changing the default application for the file type.
For images, the “Windows Photo App” shipped with Windows 10 can’t print without user interaction. Changing this to the “Windows Photo viewer” will solve the issue. If this isn’t available on your system installing a third party image viewer like IrfanView can help.
For more technical details have a look at this Microsoft article Verbs and File Associations.