There are several apps where you can download and save your PDF-files from mail, e. g. Evernote, Dropbox, SkyDrive, Kindle, ... If you have one of those on your iPad you can transfer your files there and store them.
All you have to do is open the file in your mail, tap the button shown on the picture below, then you will see, which apps open it.
When you get a .jpg image in your e-mail, you should be able to press on the image. Then, you will get a pop-up that includes the option to "Save to Camera Roll." If you select that option, it should then be saved in your Photos app (the flower icon).
If that's not happening, please let us know - we can try to help figure it out. Else, I hope this helps.