You can find a list of file types accepted by D2L submission folders here.

Other things to keep in mind:

1. Files should be 2 GB or smaller.
2. Pages documents will be accepted, but they can't be read from within D2L or used with annotations. To avoid this issue, save Pages documents as .doc or PDF, or download and install Word (available for free to students).
3. If you're uploading an HTML document, zip the file to prevent the code from being stripped.
4. If you have a Word document with tables, save the document as a PDF to ensure that the tables display when previewing the file in the grading window. D2L's document previewer doesn't always render tables in .doc files; that's why we recommend converting the file to a PDF.
5. If you received an "Oops, your file could not be uploaded" error message, even when uploading a supported file type, please see this post.