I exported a project as a pdf by clicking Save As under the file menu, then I saved the original psd by choosing Save As again and selecting PSD this time. When I came back to the project today all the layers had been merged into one. I _never_ merged them myself. Is there any way I can recover all that work or have I been hosed by this "feature"?
Hi and welcome to the forum. The answer to your question depends on whether you have closed the image file in Photosho since you di the Save as. if not you can step back through History. If that is the case, then open the History panel from the Window menu. If you have closed the file between the save as, and noticing the problem, you are out of luck. It is a good idea to use a different name when saving a PSD file as a JPG or PDF, because there is always the chance you will do a reflex Ctrl/Cmd s later on, and overwrite the PSD file. I have done it myself more than once.
Is there any way I can recover all that work or have I been hosed by this "feature"?
You have very probably messed up yourself; as Trevor mentioned others have committed errors on such operations, too, but trying to lay the blame on the application will do you little good.
If you save a copy off of a file you may want to check »As a Copy« when doing the Save As in the future, that way the open document stays the file it has been before.