Export your Google Docs to EPUB format.

In an update coming soon to Google Docs, users will be able to export documents to EPUB publications "allowing people to consume long-form content in their preferred apps on a diverse range of screen sizes and devices, including smartphones, tablets, and eReaders." 

EPUB is short for Electronic Publication, an open eBook standard that is widely supported and one of its features is support for reflowable document, which adapts text when a "page" is resized. In comparison, a PDF file page is fixed and cannot be re-sized and is kind of a pain to read. 

Exporting a file as EPUB in Google Docs is very easy. Simply go to File menu > Download as > EPUB Publication (.epub).

Head over to Google Play Store to verify if the update is available for you to download.