What does this error message, "Document is not a well-formed PDF document" mean?

• The ECF system only accepts documents that have been converted to Portable Document Format (PDF). 

• Either you did not convert your document or an error occurred during the PDF conversion process.

• If your document is already a PDF file, try converting it again and then re-filing it.

• If you have not converted your document yet, see Convert Your Document To A PDF File for assistance.