Hi,

If you used online channels to download a book After successful downloading of pdf you will get notification you can click on it to open it. another way is go to chrome browser there you can see three dot icon on your top right side click on it you will find downloads option there click it. there you can see list of files you downloaded. other way is open your file explorer search for specific  book file you want with name of it. If can not find in these ways the file may be queued. try to re download it with good internet connection