PDF was created by Adobe Systems in 1993 and has been published in several versions since then. Standards based on subsets of the PDF specifications have also been published. Below follows a list of PDF versions and their status as an Open Standard.
While specifications were available, Adobes own versions of PDF were never submitted to ISO or recognised as Open Standards. However, several Open Standards were based on subsets of these versions and have been approved by ISO. See below for more information on the different subsets of PDF.
PDF 1.7 is an Open Standard, approved as ISO 32000-1:2008. It should be noted that although Adobe Systems allows royalty-free use of PDF 1.7, other companies hold patents that may or may not encumber the standard. See below for more information on the patent claims concerning PDF.
The extensions are not part of ISO-32000 but may be proposed in the next revision of the format.
The PDF/X standard, originally based on PDF 1.2 and since revised several times, was developed by the American National Standards Institute's (ANSI) Committee for Graphic Arts Technologies Standards. It primarily serves as a colour-reliable document exchange format for the printing press. All of its currently ISO approved variants qualify as Open Standards and are published under ISO 15930:
PDF/A is a subset of PDF 1.4 specifically designed for archiving purposes. It qualifies as an Open Standard and has been approved as ISO 19005-1:2005.
PDF/E is a subset of PDF 1.6 specifically designed for engineering drawings. It qualifies as an Open Standard and has been approved as ISO 24517-1:2008.
While Adobe Systems grants a royalty-free use of any patents to the PDF format, in any application that adheres to the PDF specifications, other companies do hold patents that may limit the openness of the standard if enforced.