How to Add a Document File and Use the Name Field
If you upload a document such as a PDF or Word doc, you can use the "Insert from Media Library" editor tool, and this will let you enter a "Name" for the file that will appear on a web page you add the media file to. See screenshot below.
Select "Document or File" under "Add or select media", Choose File, and enter a word of phrase which would be a good name for this file in the "Name" field. Make sure the new file is selected (check mark appears), and the click on "Insert selected". See screenshot below.
The file will then appear in your text as a new paragraph with the name you have given it. See below screenshot.
If you need to edit the name of the document after inserting it, go to "Content --> Media --> Media Library" in the top admin toolbar, find the file and then click the "Edit" pencil icon, and edit the name.