A proprietary format is a file format of a company, organization, or individual
- that contains data that is ordered and stored according to a particular encoding-scheme, designed by the company or organization to be secret, such that the decoding and interpretation of this stored data is only easily accomplished with particular software or hardware that the company itself has developed. The specification of the data encoding format is not released, or underlies non-disclosure agreements.
Or a proprietary format is file format
- whose encoding is in fact published, but is restricted (through licences) such that only the company itself or licencees may use it.
In contrast an open format is a file format that is published and free to be used by everybody.
Proprietary formats are typically controlled by a company or organization for its own benefits, and the restriction of its use by others is ensured through patents or as trade secrets. It is thus intended to give the license holder exclusive control of the technology to the (current or future) exclusion of others. Typically such restrictions attempt to prevent reverse engineering, though reverse engineering of file formats for the purposes of interoperability is generally believed to be legal by those who practice it. Legal positions differ according to each country's laws related to, among other things, software patents.
Privacy, ownership, risk and freedom 
One of the contentious issues surrounding the use of proprietary formats is that of ownership of created content. If the information is stored in a way which the user's software provider tries to keep secret, the user may own the information by virtue of having created it, but they have no way to retrieve it except by using a version of the original software which produced the file. Without a standard file format or reverse engineered converters, users cannot share data with people using competing software. The fact that the user depends on a particular brand of software to retrieve the information stored in a proprietary format files increases barriers of entry for competing software and may contribute to vendor lock-in concept.
The issue of risk comes about because proprietary formats are less likely to be publicly documented and therefore less future proof. If the software firm owning right to that format stops making software which can read it then those who had used the format in the past may lose all information in those files. This is particularly common with formats that were not widely adopted. However, even ubiquitous formats such as Microsoft Word can not be fully reverse-engineered.
Prominent proprietary formats 
In alphabetical order:
Open Proprietary Formats 
- AAC – an open standard, but owned by Via Licensing
- GEDCOM – an open specification for genealogy data exchange, owned by The Church of Jesus Christ of Latter-day Saints
- MP3 – an open standard, but subject to patents in some countries
Closed Proprietary Formats 
- CDR – (non-documented) CorelDraw's native format primarily used for vector graphic drawings
- DWG – (non-documented) AutoCAD drawing
- PSD – (non-documented) Adobe Photoshop's native image format
- RAR – (partially documented) archive and compression file format owned by Alexander L. Roshal
- WMA – a closed format, owned by Microsoft
- DOC – Microsoft Word Document (formerly closed/undocumented, now Microsoft Open Specification Promise)
- XLS – Microsoft Excel spreadsheet file format (formerly closed/undocumented, now Microsoft Open Specification Promise)
- PPT – Microsoft PowerPoint Presentation file format (formerly closed/undocumented, now Microsoft Open Specification Promise)
- RTF – a formatted text format (proprietary, published specification, defined and maintained only by Microsoft)
- SWF – Adobe Flash format (formerly closed/undocumented, now partially or completely open)
- XFA – Adobe XML Forms Architecture, used in PDF files (published specification, but not included in the PDF ISO 32000-1 standard; controlled and maintained only by Adobe)
- ZIP – a base version of this data compression and archive file format is in the public domain, but newer versions have some patented features
Formerly proprietary 
- GIF – CompuServe's Graphics Interchange Format (the specification's royalty-free license requires implementers to give CompuServe credit as owner of the format; separately, patents covering certain aspects of the specification were held by Unisys until they expired in 2004)
- PDF – Adobe's Portable Document Format (open since 2008), but the specification allows some proprietary extensions
See also 
- "Mirriam-Webster's Online Dictionary". Retrieved 2008-07-11.
- ""Sustainability" Digital Preservation". Retrieved 2008-07-08.
- "Ubuntu's commitment to only include completely free software by default means that proprietary media formats are not configured 'out of the box'...including DVD, MP3, QuickTime, Windows Media, and more." https://help.ubuntu.com/community/RestrictedFormats. See also http://www.openformats.org/en5
- The RAR Archiver EULA (End user license agreement) is embedded in installation files -  - Quotation: "Neither RAR binary code, WinRAR binary code, UnRAR source or UnRAR binary code may be used or reverse engineered to re-create the RAR compression algorithm, which is proprietary, without written permission of the author."
- "tutorial: Rich Text Format (RTF)". Colorado State University. Retrieved 2010-03-13.
- "4.3 Non-HTML file formats". e-Government Unit. 2002-05. Retrieved 2010-03-13.[dead link]
- Novell (2004-11-12), Novell Files WordPerfect Antitrust Lawsuit against Microsoft (PDF), retrieved 2010-03-13
- "The Novell Antitrust Complaint (as text) & A Law About Antitrust and Standards Writing". 2004-11-17. Retrieved 2010-03-13.
- "Gnu PDF - PDF Knowledge - Forms Data Format". Retrieved 2010-02-19. "Apparently Adobe introduced something newer called XFA (XML Forms Architecture) which doesn't seem standardized."
- A Quick Introduction to Acrobat Forms Technology, 2006-05-14, retrieved 2010-02-19, "Adobe's XFA Forms is a closed standard that competes with the fully open W3C Xforms standard."
- ".ZIP Application Note". Retrieved 2010-12-24.
- "Latest OOX-ODF FUD-Spat: States Prepare to Ban Zip and PDF Files". Retrieved 2010-12-24.
- "PKZip Must Open Up". Retrieved 2010-12-24.