I recently worked on a project where we had over 50 .docx files to convert to .pdf. Now Office 2007 can do this for you, but only one file at a time. Luckily I was able to piece together some code (.net 3.5 csharp) which automated this process. Select a folder and all .doc and .docx files in the folder and any subfolder will be converted to pdf and saved with a .pdf extension.
You still need Office 2007 or later to do this – download the code here:
Disclaimer: Use at own risk. No kittens were harmed during the making of this software.