There is no definitive answer to this question since it can vary depending on the specific eBook reader or app that you are using. However, in general, most eBook readers will have an option to view the eBook in either a fixed layout or a reflowable layout.
Fixed layout eBooks are those where the content is laid out in a specific way and cannot be changed. This is similar to how a PDF works. Reflowable eBooks are those where the content can be adjusted to fit the screen size of the device it is being viewed on.
So, if you want to programmatically diffrenciate between the two layouts, you would need to check the specific eBook reader or app that you are using to see if it offers both options and then look at how the content is displayed. For example, if the eBook reader app only offers a reflowable layout, then that is likely the only option that is available.
