Surface Duo has pen support, and while a Surface Pen is not included in the box, you can use any Surface Pen that supports Surface Pro 3 or higher, including the new Surface Slim Pen that made its debut with the Surface Pro X.
Doing so will allow you to write naturally in apps like OneNote, or sign PDF documents in Adobe Reader. Here’s how to connect a Surface Pen to your Surface Duo.
Pair over Bluetooth
Step 1: Swipe down from the top of the screen to bring down the notification tray.
Step 2: Press and hold the Bluetooth icon to go to Bluetooth settings.
Step 3: Hit the pair new device button.
Step 4: Press and hold the top button of your Surface Pen for 5-7 seconds until the white LED light starts blinking. Your pen is now ready to be paired. Note: The Surface Pro 3 pen does not have an LED light, but holding the top button should still get it into pair mode.
Step 5: When the pen shows up as an available device on Surface Duo, tap its name and the pairing should complete.
If you have issues pairing, make sure the pen has working batteries, and try again. I recommend restarting Duo if it doesnt work on the first try.
Take notes
You’re good to go. I suggest firing up OneNote and putting the pen through its paces.
The Surface Guide 