I changed my visa from H1B to F1 in 2012 and after completing my education I am applying for H1B again. Now I need to get copy of my I-797 which was valid for duration 2010-2013. Unfortunately I have lost my copy. Now how do I get a duplicate? Can I approach USCIS to get it re-issued? I have heard about from I-824 but not sure if it is valid for petitions that are already expired. Also, it looks like it costs about $500 to file form I-824. Is that the only way I have? Do employers get copy of I-797? If they do, not sure if they keep it for 3-4 more years. Any help from your experience in this matter is appreciated. TIA.