How do you add files to a Template-type folder?

Supposedly, Word, PDF, and other file types can be added to Template-type folders, but how is that done? I'm not able to just drag a file into the folder, like I can for an image in an Image-type folder. Shouldn't that be possible?  It says "Unable to import files with extension '.docx' in a folder of type 'Template'."

 I can't find anything about this in the docs. I'm using Tridion Docs 13.