I have 6 pieces of a map that were sent to me (.pdfs) in 6 different files, and I want to splice them together to make a larger map. How do I do that?
Select all the files, and go Tools > Photoshop > Photomerge
Choose Auto, or if the different files are all flat, square (as in not distorted) and scaled the same, choose Reposition.
Or what I like to do now, is from Bridge, select the files and go Load inot Photoshop Layers
In Photoshop, then select all the layers, and go Edit > Align layers.
Another way (also depending on the files being flat and of the same scale, as would happen if they were scanned) is to increase Canvas size to make room, and set the upper layer's blend mode to Difference. You ten move the upper layer till the overlap goes full black.
At that point, lock the upper layer's position, and set the blend mode back to Normal.
Repeat for all layers and flatten
Photomerge is pretty good, if it works. I've found it's not too good with line drawings like maps, and if it doesn't work, you might have to manually align them. Do one file at time, and change the blend mode to difference. The overlap should go black when they are aligned.