Is it please possible the add a preview handler for PDF ?
I'm using Opera as PDF Viewer (no Acrobat Reader installed anymore).
When I use Directory Opus (best File Commander), and use the "viewer pane" (I click on a file and the preview window shows a small preview of the file) - it doesn't work because it looks like the Opera PDF Viewer has no Preview Handler support.
Read: Directory Opus Forum
(Opera user since Opera 6!)