PDF (adobe.com)

Select a color for transparency

  1. Click the Preview, 2-Up, or 4-Up button at the upper left of the document window. In 2-Up or 4-Up view, click a view other than the original.

  2. In the Optimize panel (Window > Optimize), select GIF or PNG 8 as the file format. Then select Index Transparency from the Transparency pop-up menu.

  3. To select a different color, click the Select Transparency Color button .

  4. Click a color swatch in the Optimize panel color table, or click a color in the document.