I use Nitro PDF, seems to be able to unlock anything in a PDF, allows editing of supposedly locked fields, removes watermarks, etc and makes filling in badly constructed PDF forms a doddle, if a little time consuming. The version I have is old, and there was a one time subscription to unlock the "professional" features, but it has been worth it just for the frustration it has alleviated over the years. The real fix would be for people that send out PDF forms to format them correctly, but sadly that seems to be beyond the wit of many companies that still use them (including the solicitors we used recently, who clearly had no idea that PDFs aren't really very secure).