Fortunately, there are a lot of good resources available that can do at least a cursory examination of different types of files and indicate that you might need to flag that alert for investigation. That's not as good as having a forensics analyst to hand the file off to, but it's a whole lot better than ignoring the alert because you don't have the time or training to deal with it.
For PDF files, Malware Tracker allows you upload a file (free of charge), which then gets analyzed and a report of it's findings returned to you. You can supply an email to get your findings that way (handy on a busy day as it lets you move on to the next alert while that file is analyzed) and you can also mark the file private, not to be shared on the site's recent infections list, in case it's your own internal document.
Here's an example of the email report you can receive:
Size: 925289 bytes
Type: PDF document, version 1.7
Submission: 2015-02-24 13:10:40
IP: 10.80.227.105, proxy=22.214.171.124
Detection: Clean 
The site is at http://malwaretracker.com/pdf.php.
While you're there, there are other resources that might help you at http://malwaretracker.com/tools.php.