With the upcoming Orbeon Forms 2019.2, you can set the PDF page size and orientation directly with the Form Builder Form Settings, or with configuration properties.
|PDF Options showing a landscape A4 PDF output format
So far, the Form Runner form layout has been fixed. That is, the form takes a fixed width even if you have a wider browser window. This is true whether you use the wizard view or not. With this new setting, you can opt for a fluid form width, where the form takes all the width available in the browser window. This works with or without the wizard view, as well as in the view mode.
|View Options showing the choice of a fluid width
We hope you will like these new Orbeon Forms features!