Failures are flagged clearly in the converter and your history, with a reason. The common ones:
"This looks like a scanned statement"
The PDF contains images of pages rather than text. Upload it again to convert it through OCR — scanned pages use 3 pages of allowance each. See converting scanned statements with OCR for how it works.
"This statement is password-protected — upload it again and enter the password"
The file is encrypted. Re-upload it and type the document password into the field that appears (details here).
"No transactions were found"
The PDF opened fine but nothing in it looked like a transaction table — this usually means a cover letter, a certificate, or a summary-only document rather than a full statement. Check you exported the transaction statement from your bank, not the account summary.
"The extraction service had a problem"
A transient wobble on our side. These retry automatically several times before giving up; if it still failed, waiting a few minutes and re-uploading almost always succeeds.
The good news about failures
Failed conversions never count against your page quota, and the uploaded file is deleted immediately regardless of outcome.