Why does it state in red letters DO NOT FILE underneath the "2018" in the box in upper right hand corner on the Form 4136 after I completed it?

[KrisD]

Are you E-filing or mailing your return?

[turbotraction]

E-filing.

[KrisD · Accepted solution]

This form is used to compute a credit for fuel tax. It flows to line 73 on Schedule 5, and from there to line 17 on the 1040. 

An electronic version of the form is attached to the Federal Return and E-filed. 

There is no need to mail the form in.