GD strategy derivative not generate thumbnail from pdf

Hello. I’m using Gd strategy derivative
Omeka_File_Derivative_Strategy_GD
but I think I doing something wrong. Because the system not generate thumbnail from pdf. So the solution I trying is upload one image (jpg or png) and pdf in a item. Only this way the thumbnail showing, but I want the thumbnail to be generated just by loading the pdf. Thanks for your answer.

Yes, GD cannot create thumbnail for pdf, only for images. So you need to install imagick or imagemagick.

Thanks. At present I using Omeka 2.3. What version of imagemagick do you recommend? Before when my omeka was in localhost, I tried imagemagick but I didn’t get it to work. Now my omeka is in a hosting.