How to batch convert word documents to pdf?
NOTE : the below instructions are for Macs running 10.4 or earlier, no longer works on 10.5 (Leopard), 10.6 (Snow Leopard), 10.7 (Lion), 10.8 (Mountain Lion).

Open Automator.

Create a new custom workflow. 

From the Actions panel library, select Files &amp; Folders then double-click Get Specified Finder Items. 

Add the items you wish to convert. 

Next, from the library, select Documents, then double click Convert Format of Word Documents. 

From the dropdown menu, select the format you wish to convert the files to. In our case we select Portable Document Format (PDF) 

Now we are ready to run the action. 

Click the run button in the top right of the automator window. 

Open up your destination folder and verify your files have been successfully converted.

Source: http://aseriesoftubes.com/articles/how-to-batch-convert-doc-files-to-pdf-format-using-mac-osx-automator/