Q: Somebody just e-mailed me a ".docx" file. Is this a Microsoft Word file? Why can't my copy of Word open it?

Q: Somebody just e-mailed me a ".docx" file. Is this a Microsoft Word file? Why can't my copy of Word open it?

A: You've received a document created in Microsoft Office 2007. The "x" at the end of the usual ".doc" file-name extension means it was saved in one of Office 2007's new, more efficient file formats, which older Office releases can't read without a free update from Microsoft.

To get that add-on, go to microsoft.com/office and type "Microsoft Office Compatibility Pack" in the search form. Downloading and installing it will enable Office 2000, XP and 2003 to read and write the 2007 formats.

If you use a Mac, Microsoft's just-shipped Office 2008 supports the new formats, and a free file converter for Office v.x and 2004 is available at microsoft.com/mac/downloads. Apple's $79 iWork '08 can read, but not write, these files.

Office 2007 users can avoid compatibility problems by telling Office to stick with the older formats. In Word, Excel and PowerPoint, click the round Office button at the top-left corner of the window, then click the Options button in the drop-down menu that will appear. Now click the Save category at the left of the Options window. In the "Save files in this format" menu, choose the previous format for each program: "Word 97-2003 Document (.doc)," "Excel 97-2003 Workbook" and "PowerPoint Presentation 97-2003."

Q: After my laptop was stolen, I was fortunate enough to get it back. But although I had a user password on the PC, I worry that somebody looked at my files.

A: Unless you hire a crew of CSI technicians, you can't ensure that somebody didn't snoop around your files. The best you can do is change any passwords saved on the machine and keep a close eye on your financial accounts.