Once you have more than just your notebook connected as part of your local wireless network at home to ultimately reach the Internet, there is of course the need and desire to exchange data between the devices. Sure, there are cloud services, but for those who like to keep their files and private data close to themselves there are other means.
One is a shared file system, residing on one of the computers, or, even better, on one of the better Wi-Fi access point / router models with USB connectivity in the back for USB sticks, printers, etc. The protocol of choice here understood by pretty much anything with Wi-Fi connectivity are "SMB" shares, a protocol designed by Microsoft. It's easy to set up and then reachable by all Windows and Linux computers in the network. I assume Mac's can reach them as well but I haven't tried personally.
That's for computers, though, but what about smartphones and tablets? As far as those devices with Android OS are concerned, it's actually quite straight forward. There are quite a number of apps and plugins to popular file managers available that add SMB network functionality. So while you are in your Wi-Fi cloud, it's easy to access those network shares as well. And, in turn, files can be exchanged easily as well. A PDF file can then be moved from a PC to the network share and from there to the smartphone or tablet.