Last December, Google Play Books saw an update that allowed users to upload PDF and EPUB files to their libraries from their mobile device (by way of Gmail attachments or downloads). A subsequent update to version 3.1.23, however, removed the ability to add PDFs. At the time, Google confirmed to us that the functionality was removed because it was "experimental," but we were told it would return at some point in the future.
Google is always finding ways to improve and enhance its services. Sometimes the updates are fairly major, while others a minor bump is enough to make a notable difference. The latter's the case with a new feature now available in GMail on the desktop, mobile site, and mobile app: the search function can now return results that include text inside of attachments.
Before today, you could only locate specific attachments by searching for the the filename or file type.