You can configure a variety of editors to work with ACDSee. You can then open images in said editors from within ACDSee.
  1. In Manage mode, click Tools | External Editors | Configure Editors...
  2. In the Configure Photo Editors dialog box, click Add...
  3. Browse to the image editing application and select it.
  4. Click Open.
  5. In the Name field, type a name for the editor, and then click OK.
  6. Press OK.
Then, to open an image in the external editor, do the following:
  1. In Manage or View mode, select the image you want to open in the external editor
  2. Do one of the following:
  • ​Click Tools | External Editors | Default External Editor or the name of an editor.
  • In the File List toolbar, click the External Editors button and choose Default External Editor or the name of an editor from the drop-down menu. Or press Control–Option–K.