have to upload file that can be no larger than 10mb
Please edit the problem description and check your tags: the question asks for .docx file (text document) and the tags advertise Calc (spreadsheet). This is confusing. What is the “mb” format?
I suspect that the question is about making a file a smaller size (and hence that “mb” in title and tags, related to the “10mb” in the question body; and also the “calc” tag related to “calculation of size” probably)… well - the asker is likely clueless, so I would try to answer the “reconstructed” question:
Your document size depends on its content. And only you know (1) what’s there; and (2) what could be cut away or decreased in quality.
10mb size is likely about images in the file; you could try right-click images in the document and use Compress tool - but be aware that that could decrease the image quality. Depending on the intended usage, that might be perfectly OK - or not; again, only you can tell for sure. You could edit your question to add missing information.