For this achievement, you need to collect all of the blueprints, key items, and invoices in the game.
To see your progress, from the iDroid, go to:
'Mother Base' tab > Database > Documentation
Here you will find the blueprints and key items you need to complete. You do not need to collect all the posters. The memento photos are required for a different achievement and do not affect Collector.
Blueprints
Most of the blueprints are obtained through completing Side Ops, Main Missions and Dispatch Missions. A few are also 'mission tasks', such as picking up a blueprint from a destroyed helicopter. Exceptions are marked by an asteriks.
GEIST P3
WU S333
URAGAN-5*
ZORN-KP
RIOT SMG
ZE'EV
MACHT 37
UN-ARC*
G44*
KABARGA-83*
BULLHORN SG
ISANDO RGL-220
HAIL MGR-4
BAMBETOV SV*
AM MRS-71 RIFLE
BRENNAN LRS-46*
UN-AAM
LPG-61
FB MR R-LAUNCHER
PB SHIELD*
STUN GRENADE*
STUN ARM
FLAMETHROWER
IR-SENSOR
ANTITHEFT DEVICE
GUN-CAM DEFENDER
UA-DRONE
For the URAGAN-5, search the Bampeve Plantation after M18.
The UN-ARC is in Yakho Oboo Supply Outpost after M6.
The G44 is in Ditandi Abandonned Village.
The KABARGA-83 is at Mfinda Oilfield.
The BAMBETOV SV is at Lamar Khaate Palace after M6.
The BRENNAN LRS-46 is in the mansion library during M28.
The PB SHIELD is found in Da Wialo Village during M7.
The STUN GRENADE is in the large hut at Kibiza Camp.
Key Items
Most of these items will be collected in your pursuit to 100% the game. These are awarded for completing certain missions and finishing every item with an S-rank. You also need to mark 500 soldiers and extract 1,000 but you should get these if you are building your Mother Base as you go.
The only exception is the 'First Aid Manual' which is found in Masa Village. You can collect it after completing Mission 18 (or during Mission 23 or in Free Roam after beating M18). It is in a house near the boat. You can interrogate soldiers for info ;)
Children's Reward
First Aid Manual
Master Certificate (Marking)
Master Certificate (Box)
Grand Master Certificate (Box)
Master Certificate (Fulton)
Grand Master Certificate (Fulton)
Conch Shell
Skulls Machete
Strangelove's Memento
Man on Fire (Corpse)
Handkerchief
Emmerich's Research Notes
Quiet's Examination Report
The Codename: Big Boss
Master Certificate (Standard)
Grand Master Certificate (Standard)
Master Certificate (Elite)
Grand Master Certificate (Elite)
Start of Bethlehem
Invoices
Invoices are collected from most of the major places on the map. You will find orange 'delivery points' on the ground. Approach these and you will find small invoices nearby to collect, thereby unlocking that delivery point and adding it to your network. You can now use the cardboard box on these points to fast travel!
Sadly, there is no easy way to check which invoices you have collected in a list. Head out to either Aghanistan or Africa and follow this list using your map. If you see a 'Delivery Point' icon on your map (looks like a clipboard) then you already have the invoice.
Afghanistan
Look at Afghanistan Central Base Camp [1] in the north of your map
Head SE to Seark Power Plant [2]
Head SE to Qarya Sakhra Ee [3]
Head E to Smasei Laman [4]
Head SW to Mountain Relay Base [5]
Head W to Eastern Communications Post [6]
Head W to Da Shago Kallai [7]
Head NW to Lamar Khaate Palace [8]
Head N to Yakho Oboo Supply Outpost [9]
Head SE to Wakh Sind Barracks [10]
Head S to Da Wialo Kallai [11]
Head NE to Da Ghwandai Khar [12]
Africa
Thankfully, Africa is much easier. Each of the nine main locations, excluding Ngumba Industrial Zone, has an invoice. Moving clockwise around your map:
[1] Bampeye Plantation
[2] Kungenga Mine
[3] Lufwa Valley Mansion
[4] Munoko ya Nioka Station
[5] Nova Braga Airport
[6] Ditadi Abandonned Village
[7] Kibiza Camp
[8] Bwala ya Masa
[9] Mfinda Oilfield