Create Still Image file creates a snapshot of the active viewport in a Rendered Frame Window, where you can save it as an Image file.
To create a snapshot of a viewport:
Grab Viewport
Create Still Image File.
A dialog appears that allows you to add a label to your snapshot.
The label will appear in the lower-right corner of the image.
The Rendered Frame Window opens to display a snapshot of your viewport.
(Save Image) to save your image.