When is it okay (or not okay) to install RPMs?

[Josef Lowder]

.
Trying to get 'pdftk' (pdf took kit) installed and running 
into one roadblock after another. 

Once I finally found 'pdftk' for my distro on the 'net, 
first, I saw this: 

Some package request cannot be installed: 
pdftk-1.12-2mdk.i586 (due to unsatisfied libgcj.so.6) 
Continue? 

So, I went looking for libgcj.so.6 
(which 'locate' told me was not on my system). 

Google could not find any 'libgcj.so.6' 
and the only thing close I could find was this: 
libgcj6-4.0.1-5mdk.i586.rpm

Will that work? 
I thought I would try to install it, but starting, I then saw this: 

You are about to install the following software package on your computer: 
libgcj6-4.0.1-5mdk: GNU Java runtime libraries
You may prefer to just save it. What is your choice? 
[Install] [Save] [Cancel]

I think I appreciate all the helpful caution messages 
(there have been several others along the way) but that 
last message now has me concerned.  How can one know if/when 
a called for package is going to satisfy (or not satisfy) 
one of these messages? 

And why would I be prompted to just save it instead of install it?