Canon S400 User Manual page 206

Select Orientation.
3
Click the OK button.
4
The Page Setup dialog box closes.
Selecting the paper size (for custom paper sizes)
When you use custom paper sizes, select any one of Custom1 to Custom3.
Select the command used for Page Setup in your application program.
1
Normally, click Page Setup from the File menu, and the Page Setup dialog
box is displayed.
Print Mode Settings
Using the Macintosh Printer Driver 206