You can open any file format including JPEG in ACR on the fly from Photoshop. If you use CS6, it even gives you the exact the same develop module controls that LR4 has in ACR. You can even write a script so that you can invoke ACR for a given layer from CS6.
thanks but I am missing something as I cannot get it to open in ACR from either Photoshop or Bridge. In Bridge the ACR button is even grayed out. I have gone through the Preferences for PS, Bridge and ACR looking for a setting to reset but nothing. What are the steps?
Don't need to flatten at all. You can watch the vid and download the script written by Adobe's Dr. Brown so that you can open any layer in ACR directly from Photoshop.
You don't mention which version of Photoshop you're using but in the more recent versions there is an option to "Maximize Compatibility" in the Edit > Preferences > File Handling menu.
When the "Maximize Compatibility" option is turned on, Photoshop saves a flattened version of your file in addition to the layer file; this makes it possible to later open the saved file in ACR or Lightroom. So the answer is you do not have to flatten your files; turn on the Maximize Compatiblity option in Photoshop, then when saving a file answer "Yes" when asked and the files will be available for opening in ACR or Lightroom.
