More people search for "pdf" (compared to other terms) than they used to. Over twice as many now as at the low point, back in 2007. That's in addition to the increase in overall search volume of all terms! Although to geeks PDF feels like a dated format, really it is about the same age as the web, and designed for a similar purpose - sharing documents. In 1991, executives didn't read on screens, so PDF differed from HTML by concentrating on printing. John Warnock, cofounder of Adobe, describes the vision in the very first memo on PDFs:

Imagine being able to send full text and graphics documents (newspapers, magazine articles, technical manuals etc.) over electronic mail distribution networks. These documents could be viewed on any machine and any selected document could be printed locally. This capability would truly change the way information is managed.

PDF became an ISO standard as late as January 2008, so it isn't surprising that it is increasingly popular. Right now, the highest search volume for "pdf" comes from Cuba. All the rest of the top 10 are African countries.

Just over a decade earlier, the countries most interested in PDFs were very different. Iran and North Africa at the top.

Maybe there's a particular stage of Internet access, open Government publishing or corporate reporting, which causes the search volume for "pdf" to increase in a particular country.

Here's to the PDF! Digital paper, yes, but still useful!