creating PDF on the fly

Hi, I don't know if this question was here before.. but... :-) I would like to know if someone have some experience on creating PDF files on the fly, in my new job I need to do this .. well.. actually I must do this :-) files to be generated are documents with free information for any user of our website, but some documents must have portrait and landscape pages.. I found a couple of classes but with them I only can create informs in portrait or landscape orientation then how can I create a pdf file (on the fly) that containt portrait and landscape orientation? I hope that you can understand my tarzan-english :-) thanks. Best Regards