From
Adobe Digital Negative Converter
my emphasis added:
"The Digital Negative (DNG) format
Digital Negative (DNG) is an openly published raw file specification that stores the "raw" pixel data captured by the digital camera sensor before it has been converted to JPEG or TIFF formats, along with standard EXIF metadata, date, time, camera used, and camera settings. This format is freely available for other software and hardware vendors to support.
Why convert to the DNG format?
Unlike most manufacturer-specific raw formats, the Digital Negative is an openly published specification that not only is supported by Adobe, but is also freely available for other software and hardware vendors to support. Consequently, it can be a safer file format to use for long-term archival purposes. Archiving your file as a digital negative eliminates worries that the raw file will no longer be readable once the camera format that created it becomes obsolete.
The Digital Negative specification allows for not only all of the pixel information stored in current raw formats, but also for all of the additional, proprietary metadata that many manufacturers include. The Adobe DNG Converter may, in some cases, ignore some of this proprietary metadata, and only include the basic information necessary for creating a high-quality image file.
The original raw file, however, can also be embedded in the new DNG format to ensure that proprietary metadata from the manufacturer is not lost."