Schooltas offers the opportunity to download books to your device's cache, which makes it possible to work offline in Schooltas. To do this, click the cloud next to your book:
In the iPad Schooltas App, every book you open is automatically downloaded to your cache.
In the Schooltas web version you can choose to temporarily download a book. The book then remains available offline until you close your browser.
In both of these cases, no actual pdf is downloaded to your device. This means you cannot download the pdf of a Schooltas books to save a copy of it.