PDF (adobe.com)

Preview all the pixels in the document that contain a specific color

  1. Click the Preview button at the upper left of the document window.

  2. Click and hold on a color swatch in the Optimize panel color table.

    The pixels that contain the selected color swatch temporarily change to another highlight color until you release the mouse button.

    Note: When previewing pixels in the document using the 2-Up or 4-Up view, select a view other than the Original view.