во нашлось в примере
boldAct = new QAction(tr("&Bold"), this);
boldAct->setCheckable(true);
boldAct->setShortcut(tr("Ctrl+B"));
boldAct->setStatusTip(tr("Make the text bold"));
connect(boldAct, SIGNAL(triggered()), this, SLOT(bold()));
QFont boldFont = boldAct->font();
boldFont.setBold(true);
boldAct->setFont(boldFont);