Why is it so difficult to convert XML to pdf?

Question

Could anybody explain to me why is it so complicated to create a pdf file from xml sheet? Acrobat can create XML File but when I want to do this other way round it suddenly gets complicated. I would like to find some simple application which would allow me to create a pdf file out of xml. Is it possible?

Solution

XML is a bunch of ingredients, PDF is the finished meal.

Those who know how to cook can create a wide variety of meals using the same ingredients. With a potato, he can create soup, mashed potatoes, crisps, french fries,... There's an almost endless list of possibilities.

Those who can't cook, will stare at the potato and wonder: How on earth can I turn this ugly vegetable into a nice croquette?

The answer is: you need a recipe. That recipe could be an XSL:FO file, the XHTML specification, a DocBook implementation, an XFA template,... Without that recipe, you'll never be able to turn your XML into PDF.