I know this is a ridiculous and overly complex solution, but it is necessary to make speedgrader useful. Whenever you have an assignment that requires a student to upload a file, always copy/paste this long string of text in the box for restrict file formats:
doc,ods,sxc,docx,odt,sxi,key,pages,sxw,numbers,pdf,txt,odf,ppt,xlsx,odg,pptx,xls,odp,rtf,bmp,png,tiff,jpeg,svg,jpg,tif
That is the complete list that is supported by speedgrader. That way, no matter what of those they upload, it will show up.
Source: https://community.canvaslms.com/t5/Canvas-Basics-Guide/What-types-of-files-can-I-preview-in-Canvas/t...