PDFs are the best way to provide artwork to us. You can export PDFs from most design software (try File>Save or File>Export) or you can use software called a PDF Printer to create a PDF from the print menu of ANY other software (if you have Acrobat Professional installed, you should already have ‘Adobe PDF’ in your list of printers, otherwise click here for a free PDF printer).
Any images within the file should have an original resolution of 150 dpi. Please ensure that the file has a 10mm bleed and no crop or trim marks (lines around the edges identifying where the bleed ends and the actual artwork begins).
When creating the PDF, the PDF options dialogue should appear. In this window you may have to specify the CMYK colour space. To do this, click on Output on the left hand side, under Conversion select Convert to Destination and under Destination select any option that includes CMYK