I downloaded the software to do my 2017 taxes yesterday. Do I have to mail them or can I efile? If so, how can I find my 2016 AGI

[RBBrittain]

Only the most recent tax year (currently 2018) can be e-filed. 2017 & earlier returns must be filed on paper.

[VolvoGirl]

So you don't need the 2016 AGI since you have to print and mail prior year returns.  Ignore anything the program says about Efiling.  Were you able to transfer from 2016?  Do you want to or did you fill out 2017 without needing it?