I have elucidated the dilemma regarding the doubt raised. First and foremost, I was confusing two concepts, TextEdit and TextDocument for the first contains the second, although they can be used interchangeably on any widget. On the other hand, I prefer QTextEdit, it has more features and is more versatile than QPlainTextEdit for creating a text editor and so investigated have equal performance in terms of resources used. I leave this reflection or as a solution in case someone is presented with any questions regarding this topic.