We can't find any of our tax documents, and obviously need to file an extension. But how do I complete the extension without those docs?

[HelenaC]

If you think your income will approximate 2017, use those figures. Otherwise, estimate as best you can. 

You may be able to get an IRS Wage an Income Transcript.

• Wage and Income Transcript - shows data from information returns we receive such as Forms W-2, 1099, 1098 and Form 5498, IRA Contribution Information. 
• Current tax year information may not be complete until July. This transcript is available for up to 10 prior years using Get Transcript Online or Form 4506-T.