Microsoft released Service Pack 3 for Office 2007 which is available for download from their website. This service Pack offers all cumulative updates since SP1 (contains all updates, fixes in SP1 and SP2), you don’t need to install SP1 or SP2 before installing SP3.

If you’ve installed Office 2007 in your System, you can update to Office 2007 sp3 in three ways, by using Microsoft Update, or use Office Update on the office online web site , office Update automatically prompts  you to install updates and service packs that bring office programs up-to-date.

You can download and install Office 2007 SP3 from Microsoft Download center.

Office 2007 SP3 improvements overview

Documents that require custom security trimming are not returned from alert search queries, even if the user who created the alert could see and query for these documents.
Non-Unicode characters in certain error message strings now display correctly.
Four new bibliography styles are now available in the "Word Citations & Bibliography" feature: Harvard Anglia, IEEE, APA Sixth Edition, and MLA Seventh Edition.
Chinese New Year holiday is now included in the Outlook calendar for Singapore.
Fixes an issue in which Excel 2007 sometimes crashes when you open an Excel workbook previously saved in a newer version of Excel. This occurs if the file uses a new feature that is not available in the 2007 Office system.
Fixes issues with the Pre and Post Reform rules in the French Thesaurus.
Fixes an issue in which encryption settings are not configurable when they are used with a file format compatibility pack converter and Office 2003 or an earlier version of Office.
Fixes an issue in which a crash sometimes occurs when an Excel workbook is opened in Excel and then previewed by using the Windows Explorer preview pane feature.
Fixes an issue in which Excel Slicers and Ribbon customizations are lost when an XLSX file is first saved as an ODS file, and then saved as an XLSX file in Excel 2007.

Read more details on Microsoft KB2526086

Download Office 2007 Sp3 (351 MB)