Upon receipt of a properly filed Form I-751, your conditional permanent resident status will be extended automatically while the form or I-751 petition is pending.
How does USCIS extend it? When you first file the required documents USCIS will send you a receipt notice which also serves as an extension of your status for one year. You should hold on to your green card once it expires and use the receipt/extension notice with the expired green card when traveling internationally or to show your current or prospective employer.
If you lose your expired green card or the receipt notice extending your residency for one year, then the local or closest USCIS office should provide you with a stamp in your passport showing you are a permanent resident. A stamp is also available in case your one year extension is about to end because sometimes USCIS takes more than a year to make a decision on these kind of cases.
All of this depends on your documents being properly filed, so please make sure to speak with a qualified immigration lawyer before filing.
If you have any questions regarding immigration, please feel free to call me, immigration attorney Shawn Mesa at (813) 679-5780.
Disclaimer: This information is provided as a public service and not intended to establish an attorney-client relationship. Any reliance on this information is taken at your own risk.