Starting with Showcase 2.5.3, you can now set which file types users are able to upload (via Showcase Global Options). This is a GLOBAL option only (not a per category)
NOTE: even those this option is already part of SC 2.5.2, it does NOTHING.
Attached Non-Image files have their OWN display blocks in 2 locations. You can set which location(s) you want to display (below content or sidebar block).
NOTE: This global option for display locations can be overriden on a per category basis.
Starting with SC 2.3.5, there is a NEW TAB in the Category Management. This was added to allow for expansion of Category Override functions as well as to organize the options a little better than they were before kinda scattered around. You can see vis the red arrows, the override function for this new feature.
Here is a screen shot of the File Uploader (previously only used for uploading images). As you can see, there is a ZIP file and a TXT file upload along with several images. The Constraints tell uses what types can be uploaded.
This shot shows what the Attached Files Block looks like (its based on core xenforo and actually uses the same exact syntax for displaying non image file attachments).
Here is what the same block looks like located under the Item Content.