I have found in the Dictionnaire de la comptabilité et de la gestion financière (dictionary of accounting and financial management), which the second edition has been added to the Grand dictionnaire terminologique, that the word dossier in an accounting context can be a synonym to dossier de travail, given as equivalent to working papers.

In that context, it would be the file in which an accounting professional would organize his papers concerning his methodology and execution, the procedures he used and the conclusions he drew. All in all, it contains just about the whole of his report.

A dossier can be translated into folder or file in all its contexts.

A dossier is a folder on a PC (ie, on the desktop)
A dossier is a folder when discussing a physical folder used to organise documents.
A dossier is a file when discussing a certain project (ie, Who is managing the J. Blow file?)

Depending on the context of the phrase I suppose it could refer to a company’s portfolio but without an example it is hard to say.

I guess it is a portfolio (collection of bonds or stocks, etc.), but no evidences to support it – sorry 🙂

«Dossier» seems to be used in financial markets both in the general senses of a “briefing” by a broker or else as a “file” (see sense #2) as suggested by others above. Also, specifically in the case of the «bourse» it is a sort of prospectus outlining the instruments and risks and terminology.

Unfortunately it’s not defined in the otherwise useful Lexique Finance

«Dossier» me semble d’être utiliser en domaine de la financier à la fois comme d’un conseil donné par un courtier fiancière et comme un ensemble des fiches pertinant à un sujet (voir #2) comme les autres reponses ci-dessus ont suggeré. En plus, dans le cas spécifique de “la bourse”, c’est un type de “prospectus” qui explique les risques et la terminologie.

Malheureusement ceci n’est pas defini par, l’autrement très utile, Lexique Finance.