What is PDF ?
PDF file is used to capture specific document in a way such that its layout and structure can be reproduced with high fidelity. PDF files are a good format for typical documents that require sharing. it is guaranteed that the display or layout of documents will be maintained for all devices. On any computer, there is a storage device where the files are saved and there is a display device which presents the file to the user and shows all the file contents.
How was the PDF file format made?
First, PDF (in 1993, twenty years ago!) was the first technology/format to serve as a way to store & transport text, vector and raster images exactly the same way regardless of platform/hardware. However, after it was released there were some attempts to compete with it – but all of those companies and formats have since disappeared.
Second, PDF is NOT a subset of Postscript. In fact, the only thing they share is the imaging model. PDF is a binary structured file format while Postscript is a programming language (that also serves as a page description language). Even the actual page description piece of PDF isn’t the same as Postscript (though it borrows the concepts!)
Concurrent with the release of Adobe Acrobat & Reader 1.0, the specification was published. So while it was proprietary, it was also published and open to all to use (even the patents were made available on a free basis!) This is how open source tools such as Ghostscript and PDFlib have been able to support PDF for most of those 20 years.
Now to answer the actual question :).
John Warnock, one of the founders of Adobe, recognized the need to have a way to view content on all screens in the same way that they looked on print. He wrote about this in his famous Camelot Paper (Page on Adobe) and started up a team at Adobe to deliver products for authoring and viewing this technology. The end result – PDF and Adobe Acrobat.