Open vs. proprietary formats

In order to work with a file, you will need most of the times some application allowing you to read, edit and save the data contained in this file.

OPEN FORMAT - We will say that a file format is open if the mode of presentation of its data is transparent and/or its specification is publicly available. Open formats are ordinarily standards fixed by public authorities or international institutions whose aim is to establish norms for software interoperability. There are nevertheless cases of open formats promoted by software companies which choose to make the specification of the formats used by their products publicly available.
It should be noted that an open format can either be coded in a transparent way (readable in any text editor: this is the case of markup languages) or in a binary mode (unreadable in a text editor but thoroughly decodable once the format specifications are known).

PROPRIETARY FORMAT - We will say that a file format is proprietary if the mode of presentation of its data is opaque and its specification is not publicly available. Proprietary formats are developed by software companies in order to encode data produced by their applications: only the software produced by a company who owns the specification of a file format will be able to read correctly and completely the data contained in this file. Proprietary formats can be further protected through the use of patents and the owner of the patent can ask royalties for the use or implementation of the formats in third-party's software.
Terminological note: we call here proprietary what others call closed; We do not mean to suggest by our terminological choice that everything that is not proprietary should be a public standard. We stressed in the paragraph above that there are many formats with a public specification (="open") which have been developed by software companies. The difference between open and proprietary (or closed) only consists in the availability or non-availability of a public specification of the format.