Hi JWF,
Yes, it is possible and not difficult. In both cases, however, the files must first be copied to some web location. Most users have a vanity space allotment from their Internet Providers.
Then, for PDF files (or any hyperlink) when composing your message in the editor, first select a piece of text. Once highlighted, look above to that middle row of icons for the one that looks like a chain. Click that and a dialog box should open where you can paste the hyperlink address to the proper field. Here's one of my essays (on WT dishonesty) that's located on my vanity space.
For photos, no text selection is necessary. Place your cursor where you'd like the photo to appear, then click that icon in the same middle row, the one that looks like a green tree. Again, a dialog box should open where you can paste the hyperlink address. Many users first place their photo to the free service PhotoBucket. What follows is an infamous image of Russell's grave site I just found using Google images. I then selected it and used the center-alignment icon.
Hope this helps.
Len