PDF (adobe.com)

Save a file in PNG format

You can use the Save As command to save RGB, Indexed Color, Grayscale, and Bitmap mode images in PNG format.

Note: You can also save an image as one or more PNG files using the Save For Web & Devices command.
  1. Choose File > Save As, and choose PNG from the Format menu.
  2. Select an Interlace option:
    None
    Displays the image in a browser only when download is complete.

    Interlaced
    Displays low-resolution versions of the image in a browser as the file downloads. Interlacing makes download time seem shorter, but it also increases file size.

  3. Click OK.