Yeah, after investigating, it seems that to run the 32-bit executable in Ubuntu 64 bit, you need to install the ia32-libs package, which is something I install routinely anyway.
(I just tested that with a LiveCD--actually it was a Linux Mint live CD, since that's the only 64 bit distro live CD I had available--but installing that and no additional packages I was able to run sopdf. I doubt it's any different for Ubuntu, since LM is based on Ubuntu.)
I don't know whether or not there's anything equivalent to ia32-libs for Fedora. I found
this when Googling, but it looks like it might be worth a shot if you can't figure out a way to compile the source.
No, I don't know anything about the sopdf source; I don't even know C.