While your case for adjustment of status is pending and you want to travel abroad, you need to apply for an Advance Parole. It will enable you to return back to the U.S. after traveling abroad without giving to obtain a visa to enter the U.S. While you travel, your pending adjustment of status will be preserved. You must be granted Advance Parole before leaving the United States. Even if you have an advance parole document, your departure will still trigger the bar to inadmissibility (3 or 10-year bar) if you accrued more than 180 days of unlawful presence.