I’m not sure if this is a real trend, or just the particular clients I’m working with lately, but I’m seeing a scourge of PDF’s intended as content for web pages. Just don’t do it. Please. Some common offenses:
“Here are my 27 PDF’s, which are every sales brochure my company has, and I want them on page X”. If someone wants to read 27 PDF sales brochures (and that’s a giant “if”), each 20 pages long, please – at least warn the visitor. Tell them that they need the Acrobat reader to read it. Most people do have it, but many still do not. Also warn them of the size – I had a client whose PDF collection included some 20+ megabyte whoppers. Even if the person is on a fast connection, this will take a lot of time to download, confusing the visitor, and may even crash their browser. Annoying the visitor isn’t going to make the sale. Also, sure, those 544 product characteristics are near and dear to your sales heart, but why not just give a nice teaser on the website, and “call or email for more info”. People looking at a webpage don’t like reading long long long pages. Honest.
Another more benign thing is giving the developer PDF’s that contain the text you want on your pages. Unless the developer has Adobe Acrobat (and many do not), it just makes it more difficult to transfer the content. The longer it takes, the more it will cost! Word documents are more or less OK, as long as you don’t assume that your exact Word formatting will appear on the website. The idea is to make it fairly easy to work with the text for your pages.
Plain emails may work, but even then you have to be careful. Let’s say you make multiple paragraphs with bullet points and quotes. The indentation, bolding, and paragraphs may not make it to your developer – there is little consistency between email programs, whether they be web-based, like Gmail or Hotmail, or installed pop clients like Eudora, Outlook, etc.
A really weird one cropped up with a recent client – mistaking PDF for web design. The request I got was “make the website exactly like these PDF’s”. The PDF’s did look awful, but if I’m asked to make an awful looking website, I can certainly do it. It just won’t appear in my portfolio. 
But here’s the deal… a website is not as precise a publishing platform as paper. Sure, maybe your site looks a particular way on your one computer, but there are many ways people look at a webpage – they have different size monitors, different computers (Mac vs. PC and more), different browsers, different screen resolution, Blackberries, cell phones, etc. Therefore, no matter what the web developer does, it will not, repeat, will not look exactly like your PDF on all computers. A very simple example is that a particular fancy text font in PDF will not be found in any normal browser – so you’ve already lost your “look”.
This is not the end of the world – what you want to do instead is make something that will look good on as many computers as possible, even if it’s not identical. Your web developer can help you with that.
That particular project required many re-do’s, because my intent was, as above, to make the page look good in all the most popular browsers. With each iteration, they insisted that it didn’t look exactly like each PDF on their PC’s. My admonitions were ignored, so I just kept chipping away until they finally liked it. As a result, it took about 4 times as long than if they had simply worked with me. And of course, those are billable hours.
I wondered why this PDF obsession is upon us, and I think it’s a couple things. A PDF allows someone a degree of control that a webpage does not. Because the Adobe reader is a separate application, it doesn’t have to deal with wildly variable website code – its only job is to display a PDF. As such, it will look more similar on different computers. But see section on “20+ megabyte whoppers” above.
And here’s a possible scenario – people are just excited with their new toy, Adobe Acrobat, and wow, they can instantly be a “designer”. They fall deeply in love with the thing they just made, and don’t want it to change. So any comments from a web developer will be taken as offense or ignored.
It’s just human nature at work. I think that many bad web designs would have been immediately discarded if people read Web Pages That Suck or Jakob Nielsen’s articles. Go there to find out what makes a good (or bad) website, for free! Doing so may even prevent your site from becoming the Daily Sucker!