This achievement is very confusing, as this does NOT pertain to obtaining dossier information. Instead, this achievement is for buying nearly all of the Intel in the game through the Clearinghouse. From the very beginning of the game, make sure that you always buy all of the Intel right away whenever you get a new mission.
Certain decisions in the game lead to more Intel being available depending on how you handled certain situations, or depending on the order in which you go through the game. Certain things, like arresting Nasiri, befriending Steven Heck before fighting Brayko, befriending SIE or Albatross before the Embassy mission, gaining the respect of Steven Heck, Hong Shi, and Albatross during the Taipei missions, and even more will give you more intel per mission.
You'll know you're getting close to this achievement if you unlock the perk "Be Prepared".