Waiting for visa extension in U.S and sending full documents to Buffalo office

[cheerup]

Hi all, i need quick comments from you as to how does my full application effect if i send "just a reciept" of extension application filed for my existing U.S H1b visa. Would they Buffalo office ask for actual renewal of my visa or just the USCIS reciept will be good to prove legal status in U.S.

Thanks all.