generate a thumbnail with imagick and place a logo on top

Hello, I have a problem creating thumbnails with imagick. The code is working ok and the thumbnail is generated in the right size etc but when I try to place a PDF logo on the thumbnail it turns half transparent. I guess it has something to do with that the PDF file is generated in InDesign and probably hasn't any background defined. Has anyone come across this problem or has an idea what to do about it? I tried to put a white canvas in the background but that didn't help. I also specified a channel for the compositeImage function but that didn't help either. This is the PDF file I'm having issues with: https://dl.dropbox.com/u/13712643/Case_Study.pdf <http://95.119.206.251/Case_Study.pdf> The generated Thumbnail looks like this: https://dl.dropbox.com/u/13712643/Case_Study1.jpg <http://95.119.206.251/Case_Study1.jpg> The code I have produced so far: http://pastebin.com/74CYC972 <http://pastebin.com/74CYC972> Thank you for your help. All the best, Andreas