Hi mohanroyal,
Thanks for posting on Apple Support Communities. We see that you are having trouble adding a signature with your trackpad when using Preview on your Mac. The Mac is up to date and this started after the most recent update.
Is the trackpad exhibiting any other functionality issues? Have you tried restarting the Mac and the trackpad? You may also want to try unpairing the trackpad and then pair it again. For assistance unpairing the trackpad refer to the section titled Remove a Bluetooth device from you Mac in this article, Using a Bluetooth mouse, keyboard, or trackpad with your Mac. Then see the section titled How to set up current Apple wireless devices in this article, Set up your Apple wireless mouse, keyboard, and trackpad.
If the issue still persists, try logging into a different user account on your Mac and test. If you don't have another user you can create one just for testing purposes. Set up users, guests, and groups on Mac.
We hope this helps!
Cheers!