The way to upload a file to Mendix is done using the built in Mendix system.document entity. If you follow the instructions in the How-to guide here you can see how to create a document upload location pretty easily.
Is there more that you want to do with your document than simply store it in Mendix for later download? A lot of times people want some way to view uploaded pdfs. If this is the case, check out the File Document Viewer in the Mendix app store
If you want to edit the word document directly in the Mendix application, that is a much more complex request and I would recommend you leverage Microsoft Office Online and open the document there.
Hope this helps,