How can I stop overlapping textboxs when I add new line on Adobe Acrobat?

These "boxes" are Acrobat's way of trying to organize text. In a PDF file, you do not have a concept of paragraphs or headers or any other organizational mechanism our brain uses to make sense of set of a page. Sometimes Acrobat gets it wrong, and then unfortunately, there is nothing (or not much, see below) you can do about that. In general, if your document was created using Adobe Acrobat from e.g. an office application, these boxes behave more the way we would expect them. If you are using a PDF generator that makes it harder for Acrobat to organize text, then you end up with a lot of head scratching.

As Bernd suggested, the best way to edit a PDF file is always to not have to edit it at all: Make all your edits in the original application and then create a new PDF file. If that is not possible, sometimes you end up with better results if you try to export the PDF file as a Word document and then edit in Word. Another option might be to completely remove the section in question from your PDF file and copy and paste formatted text from a Word document into your PDF file.

Edit the original document and create a new PDF file.