Adobe finally figured out how to make PDFs make sense on a phone

When screens got small, faithfully replicating paper documents became a problem. Enter the Acrobat Reader’s new Liquid Mode.

Adobe finally figured out how to make PDFs make sense on a phone
[Image: courtesy of Adobe]

In the beginning, there was the 8 1/2-by-11-inch piece of paper, a standardized size for documents of many kinds. (In the U.S. by the early 20th century, at least—if you know for sure when it became the default, please let me know.)


Then, in 1993, came Adobe’s Acrobat software and its PDF file format. They solved the problem of putting a document on your computer screen that precisely matched the look and feel of its dead-tree version and could be easily shared, beating out several competing products that tried to do the same thing. Twenty-seven years later, PDF has defied would-be PDF killers, critics, and prognostications of its impending irrelevancy to remain ubiquitous. Currently, there are two and a half trillion PDF files out there, reckons Adobe; a half-billion people use its Acrobat tools even though PDF is an open standard supported by countless third-party alternatives.

But as useful as Acrobat and PDF are, they have had an uneasy relationship with the 21st century’s defining device, the smartphone. Squeeze an 8 1/2-by-11-inch document onto a phone screen, and it’s likely going to be too teeny-tiny to read. You can blow up bits of text to a legible size, but that’s hardly something anyone wants to do for more than a paragraph or two at a time.

And Adobe knows it. “The experience of consuming and creating PDFs on these modern mobile devices just sucks today,” says Abhay Parasnis, the company’s CTO. “I mean, it’s really bad. I have to pinch and zoom. It really doesn’t render well. I have to pan around.”

Shrink a richly formatted PDF page down to smartphone size, and it becomes a recipe for eye strain. [Image: courtesy of Adobe]
The company finally has an answer to this long-standing everyday conundrum. It’s a new feature called Liquid Mode, which it quietly added to the iOS and Android versions of Acrobat Reader and is now officially announcing.

Unlike anything in previous versions of Reader, Liquid Mode—which you invoke by tapping a drop-shaped icon—intelligently formats documents for smaller displays. Instead of being laid out in fixed pages, everything becomes a single scrollable column of text and images, with an outline that lets you tap to jump from section to section. In short, it moves beyond the tyranny of a particular document size and makes PDFs feel more like web pages. (Web designers solved this issue years ago with responsive design, which lets websites rejigger themselves on the fly for screens of any size.)

Rethinking Acrobat for smartphones required Adobe to call on some of its latest AI tricks—it brands them as “Sensei” technology—to deconstruct documents into a form that could be reassembled on a small screen. Perhaps as important, the company had to deconstruct Acrobat’s original value proposition. A product that was once about absolute fidelity to the printed page now is taking the liberty of rearranging and reformatting elements in the interest of a better experience.


In its initial form, Liquid Mode is a first pass at a long-term challenge. It doesn’t yet support some of the most familiar types of PDFs, such as forms, slideshows, scans, and files that are over 10 MB or 200 pages. It also rejected the PDFs I’d made using iOS’s screenshot feature, perhaps because they were too complex. Still, when it worked, it achieved the formerly impossible: It made reading a PDF on a phone . . . actually pretty pleasant.

“As we started tackling this, we said, ‘This is hard,'” says Parasnis. “And until we solve it, we aren’t done. Even today, we are not done. But we have done enough that we’re excited to share it with the world.”

New—but not all-new—frontiers

According to Parasnis, Liquid Mode grew out of a question Adobe asked itself a little over four years ago: “What can we invent that will make PDF as successful and as relevant for the next three decades as it has been for the last three decades?” The company flirted with the idea of creating an all-new format that was “much richer, much better,” and not necessarily compatible with PDF as we know it. “We did some engineering work,” Parasnis says. But it quickly concluded that PDF’s compatibility and pervasiveness were such powerful assets that breaking them on purpose would be a mistake.

We pulled in some of our best engineers and basically said, ‘Take however long it takes.’”

Adobe CTO Abhay Parasnis
Instead, Adobe zeroed in on the specific goal of making PDFs—existing ones, regardless of who created them, and how—more conducive to viewing on undersized displays. The timing felt right, says Parasnis: “We had a insight that the latest advances in AI and machine learning, for the first time, could enable some real breakthroughs when it came to document understanding and document structure generation.”

The next step was to dig into the intricacies of teaching an algorithm to understand PDFs by showing it vast quantities of PDFs. “We pulled in some of our best engineers and basically said, ‘Take however long it takes, because this is a Herculean problem that’s worth solving,” says Parasnis.

Adobe’s solution turned out to involve the Reader app uploading PDFs to the company’s servers, where the company can throw AI at the task of breaking a document down into its component parts, such as headings, columns of text, tables, and images. Then the app reassembles all of these items into a phone-friendly scrollable view, with everything at a legible size. You can further adjust the type size and spacing to your liking, and flip back and forth between Liquid Mode and classic view.


In Liquid Mode, complex PDFs become a single, scrollable column of text and images. [Image: courtesy of Adobe]
While the current version of Liquid Mode doesn’t even attempt to convert all sorts of documents, it did a good job with the ones it accepted in my experiments. Simple files such as a PDF of a résumé or a Gmail message translated well, as you might expect. But Liquid Mode also aced a 46-page digital magazine, reflowing the text and images in a way that made sense and creating a table of contents that let me jump from article to article with a tap. All of a sudden, reading it on a phone went from something I’d actively avoid to a healthy alternative to obsessively checking Twitter.

Adobe’s Sensei technology analyzes the structure of PDF documents so it can reformat them for small screens. [Image: courtesy of Adobe]

Much more to come

As basic as Liquid Mode is at the moment, Adobe has a long list of ways it plans to build upon its first release. For starters, it says that it’s working on processing additional types of documents for display. It plans to add the capability to its Windows and Mac versions, and is developing a feature that will let you open a PDF in Liquid Mode, then share it so that other people can view it in any web browser.

Parasnis also says that the AI machinations currently carried out in Adobe’s cloud should eventually be possible on a smartphone. That would eliminate the need to shuttle PDFs back and forth across the internet, making the process more private and probably faster. (The current version doesn’t parse the substance of documents or store them once processing is done.) “Even the most advanced [smartphone] machine-learning chips from last year cannot do the kind of work we want to do locally right now,” says Parasnis. “We will get there.”

Liquid Mode generates a tappable outline of a PDF for easy navigtion. [Image: courtesy of Adobe]
While the company plans to always offer Liquid Mode as a free option within Reader, it’s also mulling over advanced features that it could reserve for its for-pay Document Cloud service, which starts at $13 a month, is built around Acrobat, and has an annualized run rate of $1.34 billion in revenue. “We want everyone to be able to experience it,” says Parasnis. “But I do think there are additional features that can then be layered on top.”

Which brings up another question: Will all those folks who read PDFs in non-Adobe software ever get the chance to view them in Liquid Mode? For now, the feature is exclusive to Adobe’s Reader app, and worth checking out even if you normally rely on an excellent third-party product such as Foxit PDF Reader, PDF Expert, or PDFPen. But philosophically, Adobe isn’t trying to offer something proprietary in order to steal users from other PDF software.

Actually, Parasnis is proud of PDF’s openness. In 2008, Adobe submitted the format to the International Standards Organization and created a royalty-free patent license. That has allowed other companies to embrace PDF, making it far more omnipresent than if the company had kept tight control over it.


It may be a ways off, but Parasnis talks about the day when you’d be able to use Liquid Mode inside something like Office—Adobe and Microsoft have a wide-ranging partnership—or even in third-party reader apps that compete with Adobe’s own. “PDF is the best example in this company of us doing broad, open things for lots of people, and yet still having a very vibrant, healthy business that’s growing extremely nicely,” he says. Exploring how Liquid Mode might fit into that enduring formula could keep Adobe busy for years.

About the author

Harry McCracken is the technology editor for Fast Company, based in San Francisco. In past lives, he was editor at large for Time magazine, founder and editor of Technologizer, and editor of PC World.