Stalker: Call of Pripyat → Quests → Latest Developments
Having received the documents and the PDA, they'll ask you to find them new security (if you come back in a couple of hours). The Dolgovtsy would be perfect for this; you just need to talk to their leader. The Svobodas could probably also be deployed to protect the scientists.
We go to the plant and find them. Seems like a simple task? Not at all. After you find the documents, you'll be attacked by a squad of mercenaries. The leader is armed (at least for me) with a G37 and wears an exoskeleton. After his death, you can take the PDA from his corpse and bring it to the scientists.
See also:
Pirate Invasion. Events in Terraria