How do I add a form to official forms required for filing

if it's not an official form you can't. you can still e-file without it provided it is one of the forms specified on form 8453. be sure to follow its filing instructions.

https://www.irs.gov/pub/irs-pdf/f8453.pdf

if it isn't listed your only option is to file by mail. are you sure the form is required? 

Thanks for the reply! It is an official form in Maine state taxes called Worksheet A. Schedule NRH instructions say to enclose Schedule NRH and Worksheet A with the Maine return, Form 1040ME. I have filled out Worksheet A in Turbo Tax and can print it if I have that form open but it does not show up under "All official forms required for filing" when I look those up to print. Seems like a software glitch. Can I somehow add Worksheet A with the other forms and schedules for filing?