Welcome to FME :) Unfortunately the answer is not a straight yes or no, it really depends how the PDF has been created.
I’ve its been ‘flattened’ down to a single layer, then probably not. If it still has lots of layers in it, then it might be possible. Without having access to the file, it’s a bit difficult to tell!
If its just a single PDF, it will probably be easier to just save the PDF as a TIFF and then crop the resulting output