Make a hole at the upper corners of the (unfolded) paper. So the fold is in the middle of the two holes.
Put the string through the right hole first.
Now measure how much thread you need. The corners of the page are bent to the inside (not to much).
Make a knot at the right hole, go through the upper rip, go through the left hole and make a knot there.
Now you can cut the sting at the length you want it.