Did you know you can use Apple’s Preview application to assign keywords to any kind of document that Preview can open? Well, you can… and it’s a snap.
You may be asking, why would I do that… the answer, is Spotlight. The keywords you assign in Preview can be read by Spotlight, so it may help you keep better track of files that you have misplaced.
Simply open your image, pdf, etc… in Preview, and then select Get Info from the Tools pull-down menu. Click the keywords tab, then the add button, and now just enter your keyword into the highlighted field. Click in the white space to finalize your keyword. Now just hit save and you’re done.
STRONG NOTE OF CAUTION: Apple’s Preview is capable of opening layered Photoshop and Illustrator files. But, when you save them again in Preview, they’ll be flattened. So don’t use this tip for those kinds of files. Flat PSD files should be fine.
Found via Apple