Buttons missing click functionality in epub pdf format

I have designed a digital publication that includes many buttons with "Open a URL" functionality.

The buttons work perfectly when viewing the published online document but when I publish the file as an ebub pdf, the click functionality of the buttons is lost. All other text-related Hyperlinks still work, but buttons are rendered like text and path objects.

Am I missing out something about constructing functional buttons in InDesing or is this a normal behaviour (button functionality not supported in pdf format)?

Thanks.