The PDF Association has an article on its site titled “What’s unique about PDF? and why PDF will live forever.” The article claims PDF is “a format of such flexibility and power that it will define the essential ‘electronic document’ concept forever.”
Forever is a long time. No one will think they mean that the last object left as the universe succumbs to entropy will be a disk with a PDF file, but what scale of “forever” gives sense to their claim? In a tweet responding to my skepticism, they offered a clarification:
— PDF Association (@PDFAssociation) October 7, 2015
We’re talking about at least a few centuries, unless a disaster destroys civilization first. After that, something totally different from computers as we know them may replace them — maybe artificial organic brains. Let’s take the year 2500 as a reasonable approximation to forever. Some people can still read Ancient Greek and Cuneiform, so it’s likely that someone will be able to decipher PDF files then.
This won’t be because of the flexibility and power of PDF, though; it will be because someone’s still interested in old documents. No one will be using PDF for anything but historical purposes then. Electronic stored-program computers have been around since the late 1940s; their entire history so far is about one human lifetime. PDF has been around for about 22 years, or the time it takes a newborn baby to grow into an adult. That’s not a lot of time compared to even a myopic definition of forever, and it’s already seen huge changes.
People tend to assume the world will always be the way it is now. Andy Ihnatko once told me that Amazon will last forever. But things change, computers faster than anything else. Imagine going back in time to 1990 and explaining Netflix or SMS messaging to anyone. Imagine telling them that in 25 years, pocket-sized computers with gigabytes of storage will fit in people’s pockets, cost a couple of hundred dollars, and be used mostly as telephones. We can’t guess what computers will be like in 2050, let alone 2500.
PDF’s main focus is on the appearance of documents. It has features for describing structure, but they’re secondary and not easy to use. In the future, the idea of fixed-layout documents may become obsolete. New formats may treat documents as abstract information, with software laying it out as needed, speaking it, or even translating it into a foreign language. EPub is headed in that direction. Computers may someday stop using 8-bit bytes or discrete files, undermining the whole present-day concept of what a file format is.
Digital preservation efforts usually focus on keeping documents alive for a few decades. Reaching any further out than that is really hard, requiring wild guesses about what will and won’t change. The safest assumption is that everything we have today will be obsolete before very long, and we should figure out how to ease the task of people peering back into our primitive times.