I just updated one of our Windows 7 computers with FileMaker Pro 14.0.4 Advanced to FileMaker Pro 14.0.6 Advanced without an issue.
Since DL100PDFL.dll is not needed for FileMaker Pro 14.0.6 nor FileMaker Pro 14.0.6 Advanced, I suspect the updater did not complete properly and the main application is still the previous version.
Have your colleague reinstall the previous version of FileMaker Pro 14, and run it to make sure it is working. You will see the DL100PDFL.dll in the FileMaker Pro 14 Advanced folder. Then, run the 14.0.6 updater, and make sure it completes, as the last few steps removes the .dll files. See if the issue still occurs.