Microsoft Office prior to Office 2007 used proprietary file formats. This forced users who share data to adopt the same software platform.^[42] In 2008, Microsoft made the entire documentation for the binary Office formats freely available for download and granted any possible patents rights for use or implementations of those binary format for free under the Open Specification Promise.^[43] Previously, Microsoft had supplied such documentation freely but only on request.

Starting with Office 2007, the default file format has been a version of Office Open XML, not directly the same as the one which has been standardized and published by Ecma International and by ISO/IEC. Microsoft has granted patent rights to the formats technology under the Open Specification Promise^[44] and has made available free downloadable converters for previous versions of Microsoft Office including Office 2003, Office XP, Office 2000^[45] and Office 2004 for the Mac. Third-party implementations of Office Open XML exist on the Mac platform (iWork '08) and Linux (OpenOffice.org 3.0). In addition, Service Pack 2 for Office 2007 supports the OpenDocument Format (ODF) for opening and saving documents.

Microsoft provides the ability to remove metadata from Office documents. This was in response to highly publicized incidents where sensitive data about a document was leaked via its metadata.^[46] Metadata removal was first available in 2004, when Microsoft released a tool called Remove Hidden Data Add-in for Office 2003/XP for this purpose^[47] It was directly integrated into Office 2007 in a feature called the Document Inspector.