As per my knowledge if you want to enable the option that anyone can upload no. of wall papers means dynamic website then store the image name only and upload by in database. and store the real image in a folder under root directory. Now you can use the wow slider to slide the images one by one. wowslider is a software which is used to make the slider. Just download the trial version from wowslider.com and install it. Now make a small slider of two or three images. To make it you have to follow the following steps:
1. open wowslider software,
2. add the images one by one,
3. set the effects i.e. which kind of slider you want to create.
4 click on publish button.
It generates a index.html page, jquery file and a css file. Now copy and paste the head section on a page of your website and put the css and jquery file in a folder under root accordingly. Now analyse body content of index.html. This is static slider. The body tag content can be generated dynamically also from database. as you have the image name in database and all images are stored in a particular folder under root directory.
Practically you can put anything whatever you want to put on your website, but logically it´s wrong to put pdf on wallpaper site. To put the pdfs dynamically you have to store the pdf file name in database same as in case of images.