Even when most users do not like to work with PDFs, still a large number of the sites use them. Why is it so?

Why PDF?
PDF is the most convenient way to use a printed content or design Online. You can simply export it from the desktop publishing software as PDF and upload it on the net. The need to break up the data into sections or creation of unnecessary links is thus avoided. Another advantage is that all diagrams and pictures are preserved along with the text.

Therefore, this format appeals to a number of big companies as the need for two designers, one for print and the other for web, is not there. In short, it can be said that people use PDFs when they do not understand web.

Need for a Plugin
PDFs required a Plugin to be used. Users need to download it and then revisit the site. PDF plugins take an awfully long time to load. One more downside is that once is starts downloading, it cannot be canceled. Therefore, most users avoid using PDFs.

The Layout is All Wrong
PDF layouts are actually virtual pages. The entire page cannot be seen together and there is always a need to scroll. PDF files often consist of a huge table of contents without any Hyperlinks. It becomes very difficult to find what you are looking for. Scrolling the pages is also very slow in PDFs.

The Reader Often Crashes
Another downside is that PDF reader often tends to crash the browser after a while especially if any of the browser's button is pressed. Hence, people do not like to revisit these sites.

Good for Printing
The area for which the PDFs are best suited is printing. In fact, it was the original purpose behind the use of PDFs, to preserve paper prints. Even the most complicated page full of graphics and pictures can be successfully preserved on web with the use of PDFs.

However, make sure that the contents that you put in a PDF format is also simultaneously available in a HTML format. Anytime you put PDF on your site, there must be another link to download PDF in case the visitor's computer does not have it.