[Page measurements for printing purposes]

How do I prepare a document if I need a line of text to be positioned at the top of the page without running the danger of having it cut off. The final page will be DIN A 4 which is 297by210 mm. (The printer needs the docs to be 303by216 mm, he will cut the pages).

The yellow line marks the safety area which as far as I understand should not be occupied. But there must be a way to position the text at the very top. Any suggestions? Is there a way to fiddle with the textbox and monitor in real time what is going on?