[BetterRed]

@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

1. I always Tag the books I add as "Just Added" (see Preferences->Add Books->Tags to apply when adding a book),
   
2. Add Books from Directories, without any pre-culling of superfluous formats
3. Use the Tag Browser to show the "Just Added" books
4. Select them all
5. Use Remove files of a specific format from selected books option to remove the formats I don't want in Calibre
6. 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