First off, it's going to be nearly impossible to find curtain rods that are low profile and small enough to fit those doors.
My solution: eye screws and dowels. Just make sure that your dowel will fit snugly into the screw so that your curtain won't shift around.
The dowel should measure just shy of the width of each panel. Now, measure the door, leaving between 1 and 3 inches on the top and bottom of each door so that the end product looks like a french door.
Mark the locations with a pencil. Screw the eyes into the door almost to the outside edges. This is important so that it bites into the edges of the wood framing around the door.
Once your hooks are in place, put the curtains onto the dowels and stick them through the eye screws on the doors.
Fluff and puff until the curtains look just right. If you want, you can embellish the curtains with a ribbon tie-back for an added touch.
An easy and inexpensive way to add charm to bi-fold doors. I'm Mrs. Fixit and it's just that simple.