PDF/A (ISO 19005-1) is the preferred file format for long-term preservation. Using the PDF file format allows files being sent to another user to open the file without any of the problems caused by using the other formats. PDF readers (e.g. Adobe Acrobat) are widely available and free to use. For further information on PDF/A see the PDF/A FAQ.

However, for creating and managing working documents and active files, Microsoft's Open Office XML (ISO/IEC 29500) (OOXML or OpenXML) and OpenDocument Format (ODF) [ISO/IEC 26300:2006] are the two of the most common XML (Extensible Markup Language) word processing formats available today. Microsoft Office and its format Open XML are ubiquitous with 95% of the market share using the application for word processing in their offices [1]. ODF, which is used by both KOffice and OpenOffice.org, is another popular choice because it is an open source format and can be used free of charge without any licensing agreements. The word processing applications can be downloaded and used free of charge.

OOXML and ODF meet the ISO's standards (listed below) for digital word processing. One drawback to these applications is that Microsoft Office, KOffice, and OpenOffice.org have trouble reading and displaying each other's formats properly. Each company offers downloadable patches, which allows their applications to read and display the other's format properly. Even with these patches, some information may not be displayed as originally intended.

Previous versions of Microsoft Office cannot read and display the new file format from Microsoft Office 2007, .docx. Microsoft offers a patch, which allows the application to display the new version properly.

Conversion to the file format PDF (PDF/A) is possible with both OOXML and ODF.

Common file extension names for ODF:
.odt

Common file extension names for PDF:
.pdf

International Organization of Standardization (ISO) XML word processing Standards

For more information see the Best Practices for Microsoft Office Documents.

[1] "More to Life Than The Office," Business Week (July 3, 2006), http://www.businessweek.com/magazine/content/06_27/b3991412.htm