Hi Angelica,
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
https://appstore.home.mendix.com/link/app/12/Mendix/Document-Viewer
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,
Rob