The PDF format has become a technological constant in our lives, and as with all technologies, surprising curiosities often arise about it. There is one format that is particularly noteworthy in this format: There can’t be a PDF that’s roughly half the size of Germany..

It all starts with one simple fact: While PDF documents don’t have a page limit, Adobe Acrobat, the main application used to view them, did have a page limit. They explained this in the article devoted to PDF format on Wikipedia.

The following is described in the PDF version 1.7 specification (Section H.3, point 177):

In PDF versions prior to PDF 1.6, the default user area size is set to 1 ⁄ 72 inches. The minimum page size allowed in Acrobat viewers before version 4.0 is 72 x 72 units (1 x 1 inch) in the default user space; maximum is 3,240 x 3,240 units (45 x 45 inches). The minimum page size allowed in Acrobat 5.0 and later is 3 x 3 units (approximately 0.04 x 0.04 inches); maximum is 14,400 x 14,400 units (200 x 200 inches).

Starting with PDF 1.6, the size of the default user space unit can be set via the UserUnit entry in the page dictionary. Acrobat 7.0 supports 75,000 User Units, providing a maximum page size of 15,000,000 inches (14,400 inches). 75,000* 1⁄72). The minimum UserUnit value is 1.0 (the default value).

Therefore, the limit that Acrobat Reader imposes is equivalent to: 15 million * 15 million square inchesor the same as 225 billion square inches, or 145,161 square kilometers.

The PDF of 145,161 km2 will cover almost half of Germany. Source: Wikipedia.

That’s just under half of Germany’s total area of ​​357,592 square kilometers, and they actually included a map on Wikipedia showing the area it would cover if this large PDF, delimited by Acrobat Reader, were available: Will occupy a large part of the German country.

Alex Chan, a software developer, delved further into the topic and set out to tackle a specific challenge: creating a PDF that would fully reach the limits imposed by Acrobat Reader.

After analyzing the structure of PDF documents, he created the first document in this format by hand, following this specification and structure, and after “playing” by adding additional shapes, changing its appearance or placing different objects on different pages, he understood it better. How did they work?

And above all he discovered How to create “monstrously large” PDFs.

To do this, it was enough to change the MediaBox parameter, which sets the width and height of the page in units. Acrobat allows you to get to 14,400 x 14,400, but the additional trick is to change the default unit, which is 1/72 but sets it to 75,000, which is the maximum accepted by Acrobat.

When I do this, managed to create a document It measures 15 million inches x 15 million inches. The resulting PDF is ready to download, and as Chan points out, trying to create a larger document results in an error message in Acrobat.

However, Chan went further and toyed with the macOS Preview app, because there is no limit to the MediaBox’s value. For example, it was possible to set a width followed by 12 zeros; This offered a length roughly similar to the distance between the Earth and the Moon.

The developer didn’t stop there and theoretically created a PDF larger than the entire universe: approximately 37 billion square light years. You can download that too if you want (and interestingly, these huge blank PDFs are very small in size, just over 500 bytes).

Image | Scary Maps

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