How can I pick up dropped weapons?

Weapons are picked up automatically just by running over them - but they will only be picked up if you are not already carrying a weapon of that type. You can only carry one weapon of each type - pistol, rifle, SMG, MG, and Heavy - and you can't drop or swap them in singleplayer mode.

However, if you enable cheats, you can equip any weapon you want. See this page for instructions on that.

Thank you!