This is a known issue in D2L. It usually has to do with how the student created the document. If the document was created in Google Docs or Pages, then exported as a .docx, it can cause an error that only renders the first page of the document, even if there are more pages in the document itself.
The best solution is to have the student open the file in Microsoft Word, save the file, then upload it to the submission folder. Students have free access to Office 365 and Microsoft Word, so it shouldn’t be an issue of access to Word. We recommend using Microsoft Word to save and create files because it has the fewest issues with D2L.
Information about Office 365 for students can be found here: https://offices.depaul.edu/information-services/services/email/Pages/Office365FAQ.aspx.
This issue has also been ticketed with D2L under PRB0044124.