A few weeks after USCIS receives your complete application, it will send you a receipt noticed called I-797C, Notice of Action. It is a very important document. It extends your residency for another 1 year while the application is pending. It is your only proof of legal status until the application gets approved and can be used for employment, travel and other purposes. You must also carry your expired green card at the same time as it has your photo on it.

Before you travel internationally, it is advisable to visit your local USCIS office and get an I-551 stamp in your passport. Bring your unexpired passport, expired green card, and your receipt notice. USCIS will take your green card, and they will stamp I-551 in your passport. This stamp will serve as evidence of your status, and will be valid for another 1 year. If your receipt notice expires before your application gets approved, you can get an I-551 stamp as well.