Given a specific width, I want to find out the height of a QTextDocument. In other words, if the QTextEdit that contains the QTextDocument is w wide, what is its minimum height h in order to fully display the document without the need for scrollbars?
Set the width for the QTextDocument object to your desired with and then call the function size().height(), this should return the height required for the width you have to give it before.
Have a look at the size() function documentation of QTextDocument class.