The fundamental rules for print files created in image processing software are:

• Please send us artwork that has been created in image processing software such as Adobe Photoshop or Affinity Photo as TIF or JPG files
• Please flatten layers to the background
• Do not use alpha channels
• Do not use clipping paths
• Save TIF files without compression, with interleaving
• Please set JPG files to maximum quality and baseline (standard)

However, if you still wish to supply your artwork as a PDF file, please use the PDF/X-3 standard