After exporting the image files from macOS Photos App, you can access those exported files in ACDSee for Mac.

The steps are :

  • Select the image files in the Photos App
  • Click File | Export
  • Choose one of the Export Options, e.g "Export # of Photos.. "
  • Select the folder to which you will export  
  • Launch ACDSee. In the Manage mode, navigate to that folder you selected in the previous step