Mostly surrenderred.
You have to realize that by the time the Red Army entered Poland, the Polish government already ran away to Romania (which was a neutral country towards Germany, and so the Polish Government officially ceased to exist as Romania couldn't allow them to take any official actions). The few battalions that didn't get the memo engaged in some skirmishes, but most just wanted the Red Army to let them join their non-existing government in Romania and other neighboring countries.
Also you have to realize that most of the population of those regions were not Polish at all, they were Ukrainian and Belorussian territories occupied by Poland, so the Red Army truly was greeted as liberators, it's not just some commie propaganda.
