Penguin UK has teamed up with the Berlin-based ebook app developer Readmill to bolster direct ebook sales.

The app allows readers to share ebook highlights and to talk to each other while they're reading, "liking" one anothers' updates and discussing the books.

The deal includes more than 5,000 digital titles – Penguin UK owns digital rights to works by authors such as Zadie Smith, Hari Kunzru, and John Updike, as well as Morrissey's Autobiography. People who buy ebooks from Penguin.co.uk will have the option to "send to Readmill". The arrangement sidesteps Amazon's Kindle and means that Penguin can retain more data on customers.

The free app, designed for iPhone, iPad or Android phones, lets readers share highlights, and supports digital conversations about books by linking reading to social media. Readers can use the app to update Facebook and Twitter when they begin reading a book, if they want to highlight passages or when they finish a book.

The novelist and digital publishing commentator Nick Harkaway, author of The Blind Giant: How to Survive in the Digital Age, was lukewarm in his appraisal of the move. He said: "Part of the point, we're told, of the Penguin Random House deal was to be able to take Amazon on. But Amazon's lead isn't just about Kindle or having been first, it's about convenience, price, and variety of products.

"It's another example of the [publishing] industry letting someone else build something that might define the market, which makes me crazy," he added. "If this is intended as a path to break Amazon's dominance, it better be followed by some rapid, startling innovation from inside the industry. And if Jeff Bezos feels seriously threatened, he may do what he's done in the past and just buy Readmill outright – unless Penguin Random House decides to bid … "

Unlike Kindle, which uses Amazon's proprietary "Kindle book" format, Readmill uses the open formats epub and pdf, and works with or without digital rights management (DRM) - software that is designed to protect copyright.

Penguin UK's ebooks are DRM-protected. The Readmill partnership excludes titles published by Random House, which completed a merger deal with Penguin in July to create the world's largest publisher, with revenue of £2.6bn.

A Penguin spokesperson said that the publisher was "always looking at new technologies, big and small, to better the experiences for our readers. Readmill … allows purchasers to read our books on devices of their choice."

Readmill was founded by Henrik Berggren and David Kjelkerud in Berlin, not long after the pair met during their studies at the Royal Institute of Technology in Stockholm. The Readmill app launched in February 2013.

In its mission statement, Readmill said it believes "reading should be open and easily sharable. It [the app] was built to help fix the somewhat broken world of ebooks, and to create the best reading experience imaginable. Readmill believes in retaining the clear, focused reading experience that you get with physical books."

Berggren said: "It's very exciting to be partnering with one of the biggest brands in publishing and to be able to help them making their offering to consumers stronger. Together we're making all of their titles available for reading in an engaging mobile experience."

• This article was amended after Penguin UK contacted the Guardian to clarify that ebooks will continue to be sold through Penguin UK website and Readmill does not allow readers to lend ebooks