Some portals still want a picture of a letter, not a .docx. Drop the document here. The page reads the XML, lays out text and images, and snapshots JPEG pages.
Use .docx, not .doc
The old binary .doc format is not parsed here. In Word: File → Save As → .docx, then drop that file. You will get a clear error if you try the old type.
Quality
The slider is JPEG quality for the snapshot. 88 is a sensible default. Lower it only if a portal has a tight size cap.
Many pages
A short letter becomes one JPG. A longer file is sliced into A4-ish pages and packed as a ZIP of JPEGs. Up to five documents in the list.
Simple reports look close to Word. Floating layouts, SmartArt and heavy tables may shift — for a pixel-perfect print, export PDF from Word.