Interview was mere formality. I was on L1A. They didnt ask for any original document except for passport. Having said that dont assume they wouldnt ask for things like birth cert, marriage cert, paystubs, emplyment letter etc. You should be prepared for that. After oath by raising hands, IO saw my passport, asked if i work for same company and then she started chatting more casually about my previous work experiences in singapore, japan, switzerland and UK. I have worked for same company across the globe. She asked few Yes/No question already filled in I485. Done in 5 or 6 mins in total.