When an end user uploads a document to Document Hub, the practice can open the document through Document Manager. If a DownloadDocument Failed error occurs, it indicates an upload integrity issue. This can occur in two ways:
Fewer bytes received than expected - the document was not fully uploaded (e.g. the upload was interrupted or timed out).
More bytes received than expected - the document data was corrupted or malformed during the upload process."
In both cases, the resolution is the same: delete the document from Document Hub/Document Manager and ask your client to upload the document again. If the error persists after re-uploading, check the client's internet connection stability and ask them to try from a different browser or device.