I think the problem is solved if you execute this command:
$ convert santillana-21.pdf -density 300 santillana21.jpg
instead your first command:
$ convert -density 300 santillana-21.pdf santillana21.jpg
Is It possible?
I think the problem is solved if you execute this command:
$ convert santillana-21.pdf -density 300 santillana21.jpg
instead your first command:
$ convert -density 300 santillana-21.pdf santillana21.jpg
Is It possible?