I've created PDF files with Photoshop, then combined them to create a 16 page PDF. Photoshop's colour profile is set to SWOP (Newsprint), with Total Ink Limit set to 235%.
The file will be printed and needs to be in PDF X/1-a format. Using Adobe Acrobat XI Pro, I tried Preflighting the file to get it into the correct format. Sometimes I get a colour warning, mostly I don't. When I tried uploading the preflighted file to the printers site I got the following: "WARNING Your file is not in PDF X/1-a format."
Assuming there is nothing wrong with the website, how can I create and check that my PDF is in the correct format?