You download it often to read academic paper, research note, even a profile of your favourite candidate on your smart phone or tablet.

But according to a World Bank study, most of pdfs are left buried unread on the servers.
Of the 1,611 pdf reports the study looked at, only 25 were downloaded more than 1,000 times in the five-year period between 2008 and 2012.

Over 31 percent of the reports the group looked at - 517 separate research papers - were not downloaded a single time.

The reason for this is because "pdfs often give up machine readability in favour of human readability".

"The basic format does not include any requirement that text be selectable or searchable," said a Guardian report.

Data presented as charts and tables is often impossible to export in any useable way.

Despite efforts to create 'pdf to html' converters, they still need human oversight to check for errors of interpretation.

According to the study, "more expensive and complex reports on middle-income countries with larger populations tend to be downloaded more frequently".