Assuming you do own right to documents, then it is simple work on Watermark On Pdf . Go to Edit PDF, And that all there too it. Likewise, you can do it on Watermark On Pdf to remove textbox once you go to Edit PDF within Watermark On Pdf . If you are asking about locked content or copyright contents you do not own right. Then you can not ask this type of question here.
Now the thing is that, if you own the copyright and can ask a court that you do not own right there will be no need to remove the watermark. The most common thing is to ask this way, You are not the actual publisher of this website, so watermark won't help you to remove content if you can't prove, or you have no evidence. For example, if you are just a blogger and have blog post that has the watermark. To remove the watermark, just contact publisher. And they are allowed to remove the watermark if they are asked directly. If you do any blog post on blog spot or similar it is the same, and you will have to get a request form from publishers. To remove watermark you just request a form by publishers that ask you for permission to use watermark. So if they ask.