The college is introducing a number of electronic/digital PDF forms to replace older hand written forms, which may include a feature to digitally sign it
If a form you are using has this feature, you just click on the signature box on the form
Then select the signature you wish to use (if there are more than one) from the popup box
If no digital ID's are displayed, then this means the computer and login you are using to open the PDF form does not have any such certificates installed.
You will need to either find a different computer with digital ID's installed or create a new digital ID using the link shown above and follow the prompts
More details here - Creating a new Digital ID
The digital ID you choose will then be confirmed and click on the Sign button
It will then prompt you to save the document - you can just overwrite the existing one or choose a new name
If you get a restriction warning - like below, you have opened the PDF file from an email as an attachment rather than saving it first
Just click 'OK' and choose a location to save the signed version
You will then see the signature block has been updated