I have a PSD file in channels and want to convert (flatten?) it to something I can email to a client to show progress on the design. How is this done?
With multi channel artwork, the easiest way I have found to provide a quicky overview is to just go into View > Full Screen Mode and take a screenshot. That will save yourself a lot of headaches, but the quality won't be great.
If the extra channels are spot colors, you can always select the spot channel(s) and select Merge Spot Channel:
The results from Merging the Spot Channel aren't always that pleasing though.
You can save as a PDF, but by default, Adobe Reader won't display the spot channels.