Hi everyone! Sorry for not replying for so long. My trip to Vietnam was without any trouble despite not having any passport. I gave the visa to the check in at the airport and the officer just stamped on it. When i left , they took the visa back and I used my green card to enter the U.S( The officer at the check in at the JFK airport was nice and joked : "Get a passport man , haha"). So there, that's my story . Thanks alot for everyone's reply about my issue.