January 29, 2026, 10:23 am | Read time: 3 minutes
A developer has disproved a long-standing assertion with an exciting—and thoroughly entertaining—project. To do so, she created an absurdly large PDF. TECHBOOK tells the curious story.
Alex Chan knows her way around programming code. This British software developer doesn’t just work in her field. In her spare time, she pursues unusual IT topics and reports on them in her blog. She recently pondered a curious question: Why can’t a PDF document exceed 381 x 381 kilometers in size? Alex Chan went in search of an answer and found a loophole—with enormous consequences.
A PDF Larger Than Germany
A post sparked her interest, claiming that the largest PDF document was almost as big as Germany. Alex Chan then began to do some research. Chan set out to challenge this assertion. It must be possible to create a PDF with a diameter larger than that of Germany.
During her research, she first came across an English Wikipedia entry. It states that it is not the PDF format itself that is responsible for the size limitation, but that the format inventor, Adobe, is the reason for the size limitation. To clarify: Adobe has set the maximum dimensions of a PDF document at 15 million inches by 15 million inches. This corresponds to the 381 square kilometers already mentioned. However, Adobe does not provide a reason for this.
Digging into the PDF’s Limits
As a programmer, Chan therefore next tried to teach herself how to create a PDF document. She immersed herself in the relevant technical literature and enlisted the assistance of ChatGPT to craft her inaugural PDF document.
The developer delved deep into the subject matter and learned a lot about certain changeable values within the program code. Two values in particular caught her eye: the UserUnit and Mediabox. When programming her own PDF document, Chan first tried to understand the unjustified limitation. To do this, she experimented with the values for UserUnit and Mediabox.
And indeed: Adobe Acrobat also ignored values for the UserUnit and Mediabox beyond the known limitation in her self-programmed PDF document. Does this confirm the accuracy of the Wikipedia entry?
A Tiny ‘Gap’ with Astounding Implications
However, Alex Chan was not satisfied with this result and continued her search. As the developer writes in her blog article, she discovered a “loophole” in the preview app supplied with Apple’s macOS operating system.
The macOS preview ignores any value changes in the UserUnit. However, there is apparently no upper limit for the Mediabox. Instead of the maximum possible value of 14,400, she simply entered 1,000,000,000,000—i.e., a trillion—pressed “Enter” and was amazed. This backdoor approach had indeed succeeded.
The macOS preview app showed a length of 352,777 kilometers squared for the document size. Such a distance corresponds roughly to the distance between the Earth and the moon—and is therefore clearly larger than Germany. Finding such a PDF document was the beginning of Alex Chan’s search.
A Passion Project Yielding Profound Insights
The developer later experimented with even larger values and generated a PDF document with an unimaginable size of 37 trillion light-years. Figuratively speaking, this is a square with a diameter of 37 trillion light-years.
Our entire observable universe would easily fit into this square. Because this value is only a mere 93 billion light-years. What began as a personal passion project for Alex Chan ultimately led to significant discoveries. Finally, the developer advises other programming fans who would like to experiment with the PDF document she has developed: “Don’t print it out!”
The German original of this article was published in December 2024.