You can do that. Have you contacted the retirement plan to request a copy? Or have you tried to import the 1099R? Have you gone to the plan's website to look for your 1099R?
Remember that an extension does not give you more time to pay. You need to pay your tax due by April 15. The extension only gives you more time to prepare and file your tax return forms.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**