Acrobat needs an eraser tool, much like the one provided in Photoshop or Photoshop Elements. I work with old pdf images of recorded documents dating clear back to the 1800's; these documents have a lot of photographic "static", shadows images left by the camera which took the image photo, and these items need to be erased to give the document better readability. It is hard to describe without watching the process. If you want a demonstration, contact me and you can log into my computer and watch my process.
Jeffrey Mirsepasy commented
It sure seems silly that this tool is no longer easily found in Acrobat.
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