That's the problem with all the pdf editors available out there. I guess adding stuff is much easier than editing existing stuff which you didn't add, and can be laid out in a gazillion ways, because PDF is a format for viewing and printing, not for editing.
I had a period when I worked with lots of documents. I could only find one fairly decent PDF editor which deserves to be called that way. I could use it to open any PDF and delete an existing element, or change text in an existing field. Sometimes things behaved funny, for example a text field can have each letter in a separate block, but I assume the tool did what it could within reasonable effort. It worked fine for me overall.
I had a period when I worked with lots of documents. I could only find one fairly decent PDF editor which deserves to be called that way. I could use it to open any PDF and delete an existing element, or change text in an existing field. Sometimes things behaved funny, for example a text field can have each letter in a separate block, but I assume the tool did what it could within reasonable effort. It worked fine for me overall.