When you first create a PlayScore document from a PDF score (see Creating a playable PDF) you have the option to select the range of pages you want to play. By default PlayScore chooses the first 10 but you can choose any range you wish.
If you want to alter that range later on, for example to play a different song in a songbook), tap the icon top right
. This shows the row of page thumbnails you saw when you first created the document.
Tip: The document always contains all the pages in the PDF. This screen merely lets you select the ones you want at the moment. You can always change this, and of course you can create as many documents as you like from a single PDF, for example to play different songs in a songbook.