Hi, Is there a place where we can attach extra documents as proof before efiling taxes?

It depends what you are trying to attach. However, as applicable in most circumstances (exceptions apply), you are not required to upload documents unless specified.

You are required to keep copies of all the documents and only incase of an audit from the IRS/state, you are required to provide them copies of the documents.

Please provide more information on the type of documents you are trying to attach and we can provide additional guidance. 

Thank you for speedy response. I am trying to attach letter from my HR to prove how many days I worked in state vs. out of state to avoid state taxes. Last year I got audited on this point. I want to proactively mitigate any audit requests from state. I have the documents so, just need a way to attach to the efiling...