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Mac 101: Preview (Mac OS X v10.5 and later) says:
Summary
Preview makes it easy to read Portable Document Files (PDFs) and open popular image files (including JPEG, TIFF, and PNG). More than just a file viewer, Preview offers essential editing capabilities, such as resizing, rotation and cropping, and even lets you add annotations to share your comments. Learn how to use Preview to work with your PDFs and image files.
found via "mac preview"
 
It is a viewer for PDF and such. Also allows you to take screen shots. Those are the two features I use most in Preview.
 
Wow, I never knew what the preview app was supposed to do. Your responses will help me begin with that app. thanks!

I have a question about the screen shot......i went to file>take screen shot. Then I tried to paste it in a Pages Document and it did not work. What am I doing wrong?
 
Is there any reason you can't figure out how to use copy paste from the screenshot within preview?
 
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