Follow the steps below to add a digital signature to your letter template:
From your letter template click 'Insert' (top bar) > 'Drawing' > '+New'
Click the arrow next to the 'Line' icon
Select 'Scribble'
Draw your signature
Adjust as you see fit
Click 'Save and Close'
Move your signature to where it needs to be
Click 'Save template' (top right corner)