Search within PDF files in Windows search

We have files on a server (just a plain Win7 server), when you search with different computers in the same folder, some computer find a result (that is within a PDF, in the text I mean) while others don't find anything.

I have check on all the computers in "Folder Options → Search → Search within files", and also installed that PDF iFilter thing but still it works on a few computer and others not. See images for example from 2 different computers:

What could be the problem / solutions ? Thanks for your help.

edit: maybe not unimportant, it WAS working on that computer that is now not working anymore. Maybe an Acrobat update or something caused the bug now ?

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