Error Uploading Artwork - Invalid PDF

If you try to analyze the file in Adobe Acrobat DC using > Print Production > Preflight.

You'll get an error message:

"An error occurred while parsing a contents stream. Unable to analyze the  PDF file"

You either need to go back to the client to get another file or you could try the following:

Once you've done that, open the file in Adobe Arobat DC and save it as a pdf/x file.