getPdftkVersion returns array instead of string

[ratoi-crysty]

It seems to be a problem with "getPdftkVersion" method. The method should return a string but instead it returns an array.

I think the problem appears because "_exec" returns an array (array('stdout' => '', 'stderr' => '', 'return' => '')) and the "getPdftkVersion" returns it directly instead of returning the "stdout" from it.