Start an image editor using the TouchUp Object tool

By default, the TouchUp Object tool starts Adobe Photoshop (if installed) to edit images and objects. To use a different editing application, specify the application in the TouchUp preferences. Choose Edit > Preferences (Windows) or Acrobat > Preferences (Mac OS), and select TouchUp on the left side of the Preferences dialog box. Click Image Editor (for bitmap images) or Page/Object Editor, (for vector images) and select the application on your hard drive.

1. Using the TouchUp Object tool, select the image or object or Shift-click to select multiple images or objects. If you change the object selection, the editing session terminates.
   To edit all the images and objects on the page, right-click/Control-click the page, and choose Edit Page.
2. Right-click/Control-click the selection, and choose Edit Image or Edit Object. (The available command depends on what is selected.)
   Note: If the image can’t open in Adobe Photoshop, verify that Photoshop is configured correctly. If a message asks whether to convert to ICC profiles, choose Don’t Convert. If the image window displays a checkerboard pattern when it opens, the image data could not be read.
3. Make the desired changes in the external editing application.
4. If you are working in Photoshop, flatten the image.

   If you change the dimensions of the image in Photoshop, the image may not align correctly in the PDF. Also, transparency information is preserved only for masks that are specified as index values in an indexed color space. Image masks are not supported. If you change image modes while editing the image, you may lose valuable information that can be applied only in the original mode.

5. In the editing application, choose File > Save. The object is automatically updated and displayed in the PDF when you bring Acrobat to the foreground.
   
   Important: For Photoshop, if the image is in a format supported by Photoshop 6.0 or later, your edited image is saved back into the PDF. However, if the image is in an unsupported format, Photoshop handles the image as a generic PDF image, and the edited image is saved to disk instead of back into the PDF.

Source: Adobe