This reject indicates that you have attached a document to the return that is not a PDF document. Identify the document that caused the reject. Recreate it as a true PDF document and reattach it before resubmitting the return.
This reject is caused by a non- PDF document that that has been saved or renamed with a .pdf file extension. An example would be a document that was scanned as a JPG image file, where the file extension was subsequently changed to .pdf. Such a file will not open in Adobe Reader and will be rejected as a binary attachment.
