Handling Page Sizes and Paper Sizes
Dorico handles page sizes and paper sizes differently.
For each layout in your project, you can define a page size in the layout options. This means that you define the dimensions of the layout. For printing your layout, you must usually choose a paper size that is provided by the printer that you are using.
Normally, the layout's page size and the printed paper size match. However, if you define a layout with an unusual page size that is not supported by your printer, such as 10" x 13", one of the standard page sizes for instrumental parts, you may have to print the layout onto a different paper size. You can change the paper size in the Page Setup section according to your needs. This has no effect on your layout's page size and therefore, does not affect the way the music is laid out.
If you do not select a specific paper size, Dorico automatically chooses a paper size that is based on your computer's locale settings. For example, if these are set to a European country, an international ISO standard, such as A4 may be used. If they are set to a North American country, one of the typical standards, such as US Letter may be used.
If you have defined a page size for your layout that is larger than a typical standard, Dorico automatically chooses the next larger paper size, provided that your printer supports this. For example, if the layout's page size is larger than A4/US Letter, A3/Tabloid is used.
If you print to a different paper size than the layout's page size, Dorico automatically scales the image to fit the paper. You can change this setting by specifying a custom scale factor in the Page Setup section.