One thing that alwasy gets on my nerves is when I go to a website to read an article and the web page turns out to just be a summary of the article with the full article in a PDF. 99/100 times, this results in me leaving the page and finding the information elsewhere. There are other variations of this: "See our website for information", and the information is a PDF file is another common one.
If I did click on the PDF, what would happen? On Windows, Adobe Reader would open up (slowly, sometimes taking as long as 5 minutes), then the PDF file would start loading. If I was lucky, it'd be in a browser tab. If I was unlucky, it'd be in a whole new window. On Linux, it'd open in Document Viewer, which is faster. However, I would then be unable to click any links in the document.
Why would anyone supply on the web, a page that needs an external application to run outside the web browser and call it putting information online? Especially when said application has had security problems in the past. It just strikes me as being very lazy.