My file will not upload.

First, a reassurance: your file isn't being "uploaded" anywhere — the tools load it locally to work on it. When loading fails, it's usually one of these:

• Wrong format. The Interior Formatter wants .docx (not .doc, .pages, or PDF). The ARC Watermarker wants PDF or EPUB. The Cover Maker wants an image (JPG/PNG). See What type of manuscript should I upload?
• The file is open elsewhere. Close it in Word (or whatever created it) and try again.
• A corrupted or unusual export. Re-export a fresh copy from your writing app (in Word: File → Save As → .docx).
• Very large image or document. Give it a moment; on a slow machine big files take time.

If a specific file never loads but others do, that file is likely the problem — re-save it cleanly and retry.