I have a different file for each chapter of a book; can PerfectIt check the whole book?

PerfectIt checks consistency within a document. So you'll get the best results if you compile the separate chapters into one document where PerfectIt will automatically check all chapters against each other.

There's no need to paste chapters together into one document manually:

• Paul Beverley has a free macro that will concatenate the document, and another that will separate it back into chapters. See Edit Faster with Free Macros.
• Editor's Toolkit from The Editorium includes similar macros for the same functions and installs them into your Word menu bar. See the Editorium website for details.