Qt: Handle 'Save Print Output As' dialog with QPainter::begin()

Question

here is a minimal reproducable example of my problem:

#include <QCoreApplication>
#include <QtPrintSupport/QPrinter>
#include <QPainter>
#include <QDebug>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QPrinter printer;
    QPainter painter;

    // this will open a file dialog to save a pdf file
    if (!painter.begin(&printer)) {
        qDebug() << "how to get the difference between 'Dialog Canceled' and 'File in use' here?";

    }
    else {
        //do the painting stuf...
    }

    return a.exec();
}

My question is - as already mentioned in the code - how do I know if the dialog is canceled by the user or the pdf file is just in use (for example opened in Adobe Reader)?

I already tried to check the printer.outputFormat() and the printer.docName() but they are both empty.