Answer
In order to select the TextSelection tool by default in PrizmDoc Viewer there are a few things you need to take into account. First, you have to click the button inside the embedViewer() function found in the index page of the sample. Second, the button for the text selection tool is actually disabled initially, so in order to be able to click it, the button has to be enabled first by removing the pcc-disabled class.
Use the following code to do this:
function embedViewer(options) {
var viewer = $('#viewer1').pccViewer(options);
viewer.viewerControl.on(PCCViewer.EventType.ViewerReady, function(viewer) {
$("[data-pcc-mouse-tool=\"AccusoftSelectText\"]").removeClass('pcc-disabled');
$("[data-pcc-mouse-tool=\"AccusoftSelectText\"]").click();
});
}