henke: PDF files can contain images, but also text, with instructions for how that text is rendered. You're right that if it's just an image, it should render fine, but note that for just images, there's no searching available. If the PDF contains text, it may also contain embedded fonts, in which case it should display properly. The type of PDF that might not display properly is one containing text in an unsupported language or with an incorrect encoding, without embedded fonts.