I-485 Approved Has't got my green card yet, Can I leave US?

Hi Teacher 8,

 

I got my I-485 approved yet haven't got my greencard. I have a letter with immigration officer's signature on it says my case is approved. I am using my EAD right now and  my company would like me to have a business trip next month.

Can I leave US and get back with my EAD card and Advance Parole before getting greencard?

I tried to schedule an interview with local office to get a stamp on my passport but there isn't anytime availble soon for me to schedule it.

What should I do?

Thanks for helping!!!