WM/Sad is a simple Word macro virus that does not do anything but replicate.
It infects the global template when an infected document is opened. After that every closed document will be infected.
Based on the settings of your F-Secure security product, it will either move the file to the quarantine where it cannot spread or cause harm, or remove it.
A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:
Check for the latest database updates
First check if your F-Secure security program is using the latest updates, then try scanning the file again.
Submit a sample
After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.
Note: If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.
Exclude a file from further scanning
If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.
Note: You need administrative rights to change the settings.
It contains the following macro description:
Installed to your NORMAL template as AutoClose to clean the prank macros from any documents that you open then close.
This description is on "AutoClose" macro in the global template, and on "Sad" macro on infected documents. It is viewable from "Tools/Macro" dialog.