Validate if an application is at the server

I have an own webserver and for one of my clients I need to be able to search through PDF's. I've asked my hostingprovider to install the xPDF package. Now I've come to testing and I'm calling this line of code in a PHP script:

$content = shell_exec('/usr/local/bin/pdftotext test.pdf -');

The only thing is, I'm getting a NULL result with. So, my question, is there a way to validate if the program is really installed? Btw, I'm not even sure if the pa开发者_如何学JAVAth is correct. I'm pretty new if it comes to having an own webserver. I've taken this example from : http://davidwalsh.name/read-pdf-doc-file-php

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If you have shell access, log in using SSH, and try

whereis pdftotext

if the only thing you get is a

pdftotext:

then it is most likely not (or not properly) installed.