Transferring an ebook to a Sony Reader is exactly the same process as transferring an ebook to any other Adobe DRM compatible ereader, so you can follow the exact same guide, once you have completed one extra step.

Without it your Sony Reader will not appear as a device in Adobe Digital Editions (ADE). As ADE will not be able to detect your Sony Reader.

To explain, Sony Readers are now no longer supported by Sony. They were manufactured from 2006 (the PRS-500) until 2014 (the PRS-T3). When they were actively supported Sony made their own software to transfer ebooks to the devices called "Sony Reader for PC/Mac". Sony removed the download for this software on March 31, 2023.

To get ADE to recognize your Sony Reader, you need to install the discontinued "Sony Reader for PC/Mac" software. You don't actually need to use the Sony software to read or manage your books; installing it simply provides ADE with the background drivers it needs to communicate with your Sony Reader.

First if you haven't already done so, install Adobe Digital Editions. Then authorise it with a ByteBooks account.

You can then install "Sony Reader for PC/Mac" (at your own risk) from the Internet Archive: https://archive.org/details/sony-reader

Note: The software works on Windows and older Intel Macs, but it is incompatible with newer Macs running Apple Silicon.

Once installed, it will give ADE the necessary drivers to detect your Sony Reader. You can now follow the standard guide for Transferring an ebook from ADE to an ereader device.