Why was my PDF rejected?

Uploads are checked before anything else happens. A file is rejected if:

• It is larger than 10MB. Scanned documents are the usual offender — re-export at a lower DPI, or run it through a compressor. Splitting a long contract into two envelopes also works, though it costs two credits.
• It is not a PDF. The upload must arrive as application/pdf. Word documents and images are refused. Export to PDF first. Note that zSign checks the content type and the file's internal structure, not the filename — the extension itself is never the reason for a rejection.
• The file is structurally damaged — a missing PDF header or a missing end-of-file marker. This usually means a truncated download or an interrupted export. Re-download or re-export the original and try again.

If a file opens correctly in your PDF reader but zSign still rejects it, re-save it from that reader ("Print to PDF" works) — that rewrites the structure cleanly.