Can a pdf file be edited? Which tool can do that?

[Kross]

It is often said that a pdf file can't be edited. I want to ask the house if there is a possibility of editing a pdf file. Which file can be uses to achieve the editing of the pdf file?

 

[King Belieal]

I know that there are online pdf editors that are used to do some small editing PDF files. One of such tool is called small PDF.