New PDF compression filter will save space, need software updates

Brotli is one of the most widely used but least-known compression formats ever devised, long incorporated into all major browsers and web content delivery networks (CDNs). Despite that, it isn’t yet used in the creation and display of PDF documents, which since version 1.2 in 1996 have relied on the FlateDecode filter also used to compress .zip and .png files.

That is about to change, though, with the PDF Association moving closer to publishing a specification this summer that developers can use to add Brotli to their PDF processors. The hope is that Brotli will then quickly be incorporated in an update of the official PDF 2.0 standard, ISO 32000-2, maintained by the International Organization for Standardization.

With PDF file sizes steadily increasing, and the number stored in enterprise data lakes ballooning by billions each year, the need for a more efficient compression method has never been more pressing.

The pay-off for using Brotli compression will be smaller PDFs. This will translate into an average of 10% to 25% reduction in file size, depending on the type of content being encoded, according to a 2025 test by PDF Association member Artifex Software.

Unfortunately, for enterprises this is where the work begins. As PDFs written using Brotli compression start to circulate, anyone who hasn’t updated their applications and library dependencies to support it will be unable to decompress and open the new-format files. For PDFs, this would be a first: While the format has added numerous features since becoming an ISO standard in 2008, none have stopped users from opening PDFs.

The most visible software requiring an upgrade to support Brotli includes proprietary PDF creators and readers such as Adobe Acrobat, Foxit PDF Editor, and Nitro PDF. PDF readers integrated into browsers also fall into this category.

Beyond this, however, lies a sizable ecosystem of less-visible open-source utilities, libraries, and SDKs which are used inside enterprises as part of PDF workflows and automated batch processing. Finding and updating these components, often buried deep inside third-party libraries, promises to be time consuming.

If enterprises delay updating, then they risk encountering PDFs created using newer software supporting Brotli that will no longer open on their older, non-updated programs. IT teams will most likely come face to face with this when users contact them to report that they can’t open a file.

Building Brotli support

To kick off adoption, developers need encouragement, said Guust Ysebie, a software engineer with document processing developer Apryse. “Somebody has to jump first and make some noise so other products jump on the bandwagon,” he said.

It’s a challenge because, as he explained in a post about the move to Brotli on the PDF Association’s website, Brotli’s adoption has been slowed because the PDF specification requires consensus across hundreds of stakeholders.

The transition can be eased in three ways, he suggested, the simplest of which is to publicize the need to upgrade across multiple information sources as part of an awareness campaign.

A more radical suggestion is that Brotli-enabled PDFs could be formatted such that, rather than cause older readers to crash, they could show a “not supported” error message encouraging customers to upgrade as a placeholder for the compressed content.

A final tactic is for likeminded developers to take it upon themselves to upgrade open-source libraries. Ysebie said he’s added Brotli support to several libraries, including the iText SDK from Apryse.

“This is how adoption works in real life: Create the feature unofficially, then early adopters implement it, and this causes bigger products to also adopt it,” said Ysebie. The critical moment for adoption of Brotli-enabled software would be its appearance in Adobe Reader. This will happen at some point, but when is still unclear, he said.

The good news is that because there are only a limited number of software libraries to upgrade, adding support to this software should be straightforward, said Ysebie. However, organizations will still have to apply those updated images to their current applications.

As to when Brotli will be added to the ISO PDF 2.0 specification (ongoing since 2015), Ysebie agreed this has a way to go. But the industry had to move on from old technology at some point. “We need to push the ecosystem forward. It will be a little chaotic in the beginning but with a lot of potential for the future.”