To print off a window card in A3 size, please follow the steps listed below:
Generate the window advert as normal and open it in Microsoft Word
Go to File > Save as > Change the file type to PDF and click Save
The new PDF document will be automatically opened
Click on the printer icon (shown below)
Click More settings
Ensure the Scale is set to Fit to printable area
Ensure the Paper size is set to A3
Click Print