Adobe PDF is the document format of choice for marketing people that completely destroys billions of attempts at communication through the Web. PDF is a fancy packaging of the Postscript printer language used as an attempt to freeze documents in a print friendly format. If you have every tried to print PDF, you know some of the many PDF limitations that make it unsuitable for print. PDF is worse for the Web, in fact PDF is the exact opposite of what you want on the Web.
Adobe try to justify their PDF file format at www.adobe.com/products/acrobat/adobepdf.html. Part of the justification appears to be very old from back in the days when every computer had a printer attached so you could print everything for filing.
PDF is Postscript
PDF uses the Postscript language to describe the look of the document instead of focusing on the content. The whole focus of the Web is to remove fixed formatting from Web pages and let visitors adjust the presentation of information to suit their needs, their computer, the limitations of their display device, allow for visual impairment, and to allow intelligent searching of the content. Postscript locks out most of that flexibility because Postscript is aimed at forcing printers to present every pixel the way the marketing people want; frozen on paper, no matter how overcrowded or unreadable or inappropriate to the reader.
PDF is Less Than Postscript
PDF takes the locked up Postscript and adds extra locks to make the information even less accessible. Try something as simple as changing the format of the output to fit a different screen format. This is totally automatic in properly crafted Web pages, is feasible in Postscript, but impossible in PDF. You have to buy an Adobe product to edit the format in PDF and you have hope that the creator has not prevented editing.
If you only want to read the PDF, with no intention to fit the document to the optimum readable format for you, then you are still faced with all sorts of problems. PDFs are read using Adobe's Reader, formerly called the PDF reader, and before that, the Acrobat Reader, but the reader is not open source which means you are stuck with whatever Adobe supply. What do they supply?
Adobe Reader Does Not Work With Your Web Browser
Firefox is the world's most popular Web browser based on people making their own choice of Web browser. Microsoft's Internet Explorer is the world's most popular Web browser based on default browsers loaded on a computer but not necessarily used. Opera and a few other browsers compete for the handheld device market but it is difficult to find a winner because so many handheld Web browsers are relabelled with the brand of the device.
From what I see among professionals who use Web browsers for work, 60 percent immediately install Firefox so they can get on with useful work and they regularly move to the latest release of Firefox, with each release compatibly with previous releases. Microsoft produced many releases of Internet Explorer with little compatibility between releases, which means you have to count almost every release as a separate browser, and only recently did they actually start catching up with the security of Firefox. It makes sense to choose Firefox because at least you know it will work without destroying your computer.
Adobe have the resources to support any and every major Web browser but their reader does not work with any of the browsers I use or any of the other browsers installed on my customers computers. Adobe deliberately limit you to downloading exactly one release of their Reader software and each release works with only one browser, Microsoft's browser, and only one release of Microsoft's browser, which is extremely difficult given that Microsoft limit you to downloading exactly one browser and not necessarily the one that works with the current Adobe Reader.
The result is Adobe reader never works reliably with a reliable browser. You find all sorts of weird error messages from Adobe Reader along the lines of
I might screw up here and I will blame it on your browser, not my sloppy program. After you click through all the warnings, the document display usually works because it is just Postscript. Try shutting down PDF after displaying a document. The reaction of the Adobe software is so weird and extreme that you have to assume Adobe have never tried to shut down their own software, have never finished looking at a document, or exited a browser. What happened to testing software before release?
Adobe Reader Does Not Work With Your Computer
When Adobe Reader screws up your browser, it does more than destroy the browser, Adobe happily take out the whole computer. Adobe Reader and Microsoft's Internet Explorer complete for the record of who can lock up a whole computer the most times per day.
To make matters worse, Adobe has decided to ignore what the world wants and suck up to Bill Gates exclusively. Given that most countries in the world choose to not use Microsoft products exclusively and many countries have almost zero use of Microsoft products, Adobe decided their latest Adobe Reader, release 8, should bury it's head in the sand and force you to reject modern software in favour of old American proprietary glue. If you love Adobe, you have to love Microsoft.
Adobe Reader tries to insult me with the following message during installation. Keep in mind that I do not use Internet Explorer anywhere, on any operating system including Windows. None of my customers use Internet Explorer on any of their computers including those using the Windows operating system.
This version of Internet Explorer is not supported. You should upgrade Internet Explorer to version 6.0.2600.0 and run setup again. Setup will now terminate.
Adobe Reader Does Not Work
Adobe clearly do not want to get off their rich fat butts and help any of their customers use PDF. PDF is an ancient ossified document format that was only ever intended to copy data from your computer to a printer and does a horrible job at that one rare task. Do not use the dinosaur on the Web.
Somewhere way back in the dim dark past, long before the 1993 debut of PDF, when the PDF format might have been useful. On day one of PDF, the format extremely limited the resolution of images included within the PDF. Publishers had to demand images be supplied independently of PDF so the publishers could print the full resolution original, not the junk included in PDF.
The image in the PDF was only ever uses as a placeholder to make space for the insertion of a good image. The PDF would be translated to the file format used by the publishing system then the good images would replace the low resolution PDF images. Some publishers would ask for clean postscript untouched by PDF while others as for the original file format, say Microsoft Word 98, with the images as full resolution TIFFs. They could then avoid the quality reduction forced by the PDF format.
There was a time when really small cheap computer screens could not exceed the maximum resolution of PDFs but that finished a long time ago. Only mobile phones have screens poor enough to not show up the faults in PDFs.
PDF is a file format that failed on medium priced computers with good screens back in the 1990s when PDF was first invented. PDF had a temporary reprieve on the very first laptop computers because of their poor LCD screens but those horrors are gone. Now the degraded images in PDFs continually show up as faulty in the cheapest computers and magazines that accept advertising in PDF format stand out as junk.
Add faulty software to faulty images and artificial limitations on the most basic uses of the file, and you get a really awful file format. Why would anyone use PDF for anything?
Adobe Reader Does Not Work on the Web
Now place a PDF on the Web where you really want great accessibility and search ability, PDF fails again.
The whole idea of presentation on the Web is to give the visitor the chance to vary font size, colour, and many other presentation aspects to fit the requirements of the visitor. This requirement for flexibility applies to the following list of people due to a whole list of reasons I will not cover here.
Many other people
The end result is up to fifty percent of people already need something better than PDF and the percentage is growing rapidly, and that is without counting the growth of handheld devices including mobile phones.
You need a document format that is flexible, fits the high quality of the best displays, fits the screen space of small devices, works with a variety of fonts, gives the user control of data display, adapts to the user's visual requirements, translates to audio presentation and Braille display, plus is searchable from outside the document. HTML does most of these things. XHTML does all of these things. PDFs does none of them.
PDF is useless on the Web. PDF is useless for presenting quality images. Adobe refuses to make the PDF Reader software work on normal computer systems. PDF should have died back in the 1990s. For the Web, convert your documents to XHTML or an Open Office document format, anything other PDF.