A DJVU document typically contains both a layer of scanned image and a layer of the text in that image. Sometimes, a DJVU document is produced which does not have the text layer. This makes it hard to search and find text in the document.
Recognising the text in the DJVU document using OCR and adding that as a text layer to that document is easy:
Download CuneiDjVu and unzip its contents.
Run the CuneiDjVu program.
Choose the DJVU document as input, choose the output folder and the OCR language.
Press Process and the resulting file will be CuneiDjVu Result.djvu on your Desktop.
Tried with: CuneiDjVu 1.4 and Windows 7 Professional x64