Because there is a business niche that PDF was created to fill 3 years ago that still exists and PDF is now so mature that it is unrivaled bypetitor formats. That niche is serving as a digital printout and a number of bordering uses. PDF main objective is precisely capturing the appearance of any document or output of any application; identically across platforms and immutably if need be. This original application spawned popularity and further feature development for professional printing archival paperless and secure business document workflows forms engineering and multimedia accessibility and many others. PDF was also the first such format adapted for Internet delivery (as was its apanying free viewer software Acrobat Reader). At the end of th 9s Adobe the creator of both worked with Netscape the then browser market challenger and innovator to develop the concept of plugins extending the browser's functionality to enable the seamless progressive display of PDF as it was being downloaded just like HTML pages. The Acrobat plugin was also downloadable for free. At the time there were no other ways to publish universallypatible and pixel-perfect replicas of carefully designed documents (or books and magazines) to the browser. That as well as PDF's adoption by the IRS in the US hugely contributed to the format's ubiquity and popularity.