MDL-49998 editpdf: Clean code to make it more readable.

MDL-49998 editpdf: Clean code to make it more readable.

There was a big proliferation and reuse of $pdf variable
that was making the code hard to read/review. This commit
does change nothing but makes it more readable.

Also adds a couple of Close() calls, not strictly needed
because they don't have opened files. But think it makes
really clearer the scope of every variable. And, for sure
it frees some resources. That cannot be bad.