Mac: Drag the ePub file directly into the iBooks library, or go to File > Add to Library and select ePub file from your downloaded ePub file location.
IBooks can be used for iOS 8 and Mac OX Yosemite and higher. It will remain saved to your local drive and will be accessible when you open Readium again.
The ePub file will load into the library for use.
To add your downloaded ePub file to Readium, click the plus sign in the top right corner of the Readium app, and select your downloaded ePub file from your device.
Click the Readium icon to open the app.
Click on "Apps" button within your browser, or navigate to chrome://apps/ in your address bar to open your Apps page.
Click "Add App" in the pop-up box to add to your Chrome browser.
Click the green button “Install Readium.
Go to: within the Google Chrome web browser.
How to install Readium and open ePub files: Recommended: Readium Extension for the Google Chrome web browser Using the Big Ideas ePub files with other eReader applications could result in a degraded experience. Please see instructions and recommended eReader applications below. EPub files require an eReader application in order to be accessed.