Inkscape has a command line conversion option.
I've only used it with a Linux instance.
It converts one page at a time though.
More than thee output format options from memory.
Not exactly pure Ruby approach, though scripting such a task is
certainly a Ruby domain.
Your example is still loading here.
So this reply may be completely out of context.

MarkT

> I have to extract some data from a paper in a pdf format. I just need
> some data from the page 1, like the title of the paper, the authors
> list, the universities of these autors, their mails, the abstract and
> keywords

I _top_ _post_ _so_ _there_