What data format does KOffice read and write natively?
As of KOffice 1.5.0, the OASIS OpenDocument file format is the native format. This allows documents to used in other applications that support the OpenDocument format, including those in the OpenOffice.org suite. Up to KOffice 1.3, KOffice applications used their own file formats. OpenDocument support was introduced for most applications in KOffice 1.4.1, but only became the default format in KOffice 1.