If a PDF reader is not installed (or the version of the software is old), an error message appears when you select "User Manual" from the "Help" menu, indicating that the file cannot be opened.

A PDF reader is not included with the VOCALOID4 Editor installation DVD. Follow the steps described on the website below to install or upgrade Adobe Reader.

Adobe Reader is available free of charge from the Adobe website:
http://get.adobe.com/reader/