To export the file to EPUB format, in the main menu select File > Export.
Select EPUB (Reflowable)
InDesign gives you the option to save as a fixed layout document or as a reflowable document. The reflowable document is a much better option for people with low vision because it allows them to resize the text, change the fonts, and manipulate the document in other ways that they need to see it adequately. If your document absolutely depends on the fixed positioning of the elements, then you can choose that option, but you won’t be taking full advantage of EPUB’s accessibility features if you do that.
Select EPUB 3.0
For maximum accessibility, select EPUB 3.0 as the version. Previous versions do not have as many accessibility features.
EPUB 3.0 is not the default option, so you will need to select it each time before you export your document.
Under the “Object” settings, you may want to choose the CSS Size option of “Relative to Text Flow.” You may need to experiment with that option, though, to find out how well it works with your particular document.
Ensure the Document has a Title
Under the “Metadata” settings, add a document title if it doesn’t have one already. If you already went through the steps to add a title to the document in InDesign’s metadata, that title will show up in the EPUB export settings.
After exporting, open the file in an EPUB reader and test it with a screen reader to ensure it retained all the accessibility features.