The dossier (emphasis on "e") is an indecipherable French word of the middle kind, meaning a selection of documents on a certain topic or about any person. They say that the FSB has a detailed dossier for every politically active citizen of the Russian Federation.
The dossier can be stored not only in paper but also in electronic form. For example, the "Panama dossier" on offshore schemes was posted to the network in the form of files.
The dossier is in the list: French words