Just to clarify any confusion, pictures of your models should be in Jpeg format.
The site will reject any other format and in particular pdf files can not be posted even though they may contain a picture.
If you really want to share a pdf file you can send a pm to the intended recipient and ask for their email address.
The pdf file can then be forwarded via email address provided.

We should all be aware of the dangers posed by shared files and unless you know and trust the source there is a real danger that malware or viruses could be hidden in the file. If you open the file and receive a message that your software is out of date don't open any links provided. Chances are it will place a fake copy plus malware on your PC that you will authorise and defeat you virus detection software.