Taking screenshot programmatically in mac only for application window

Simple.

NSImage *captureImage  = [[NSImage alloc] initWithData:[self.view dataWithPDFInsideRect:[self.view bounds]]];

please check and let me know. This is captured current active window.

To actually take a screenshot of your window, including its frame and shadow, get your window's windowNumber and pass that to the CGWindowListCreateImage function.