Microsoft has posted the final service pack for Office 2007 on their support website and the download is accessible either through Microsoft Update or you can download the package from their download center. In addition to the service pack there is also an Office Language Pack 2007 SP3 update as well.
Service Pack 3 contains all of the updates that have been released since Service Pack 2 came out in April of 2009. If your still running Office 2007 then this is a must have update. You do not need to install SP2 in order to install this service pack.
Here are some of the improvements in this update:
- 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.
KB Article 2591067 also addresses some issues you may encounter when installing Office 2007 SP3 so I recommend you have a look at that before proceeding just in case you have one of those scenarios in play.