@ChristopherLewis - Maybe you can make use of this feature
Preferences->Add Books->Automatic Adding->Ignore files with the following extensions when automatically adding
Or, perhaps you can use a process similar to this one
- I always Tag the books I add as "Just Added" (see Preferences->Add Books->Tags to apply when adding a book),
- Add Books from Directories, without any pre-culling of superfluous formats
- Use the Tag Browser to show the "Just Added" books
- Select them all
- Use Remove files of a specific format from selected books option to remove the formats I don't want in Calibre
- Delete the "Just Added" Tag
Has the advantage that its all done within the Calibre folders using Calibre functionality, without disturbing your original folders, or having to use Explorer/Finder/Nautilus to pre-prepare files to go into Calibre. And its quick.
BR