I have slightly changed the title to 27 years of PDF since I am involved with this data format already since 1991.
Then the concept of PDF was presented for the first time to the public at a Seybold conference in San Jose. On June 15th, 1993 Acrobat 1.0 was shipped. A few weeks later the PDF Reference Manual was available in the book stores.
(I necessary video quality can be increased in Settings or use YouTube- link.)