On all magazine ads, all material must be 5mm off.
This margin is also called bleed. This means that the print goes all the way to the edge of the sheet. It can be a solid color background, an image, a box or line, or other elements that extend to the edge of the sheet.
In order for us to get our print result, we have to print on a larger sheet and cut it down to the net format. The file delivered must therefore also be larger than the net format.
It is common to add 5 mm extra on all edges. When printing to PDF, you must therefore remember to print on a larger page format than the net format.
When exporting from e.g. InDesign or Illustrator keeps it marked for e.g. 5 mm bleed and crop marks.
Then the document size in the PDF file is automatically slightly larger than the original document, so that bleed is included.
It is also important that text, logos, etc. are kept well within the bleed field, so that it is not cut away during pruning.