It is possible to upload the binary file in the process of building the link to it, but it is usually best to choose to upload the binary file in advance (and then later build the link to it), as described here:
Login and navigate to the page on which the link is to appear; select "View Page in CommonSpot," "Work on this Page," or "Work on this Page (All Changes)." This ensures that the uploaded document will be password-protected, or not, consistent with that subsite's pages. Once in a while, you may have to adjust the document's security settings, but usually the subsite default will be appropriate.
Click on the "New" button on the full-width toolbar and select "Uploaded Document...".
Select the subsite into which to upload the document; it should default to the current subsite; click "Next" at the lower right.
Click on the "Browse..." button and select the file.
Provide a title that is terse, descriptive, and unique; complete the rest of the "Upload New Document" lightbox; click on "Next" in the lower right.
The lightbox will close when the upload is completed.
Next, build the link, making the choices appropriate to link to an already-uploaded document, as discussed separately.