DJVU was developed about fifteen years ago and is a very successful blend of test and graphics formats. If you have a file with the djvu extension lying around on your computer, know that this is not a program or a picture, this is an e-book. You can't just open it - neither in Word, nor in any other text editor, since the format itself is rare and specific. It contains copies of paper books, manuals, magazines and other publications made on a scanner. This method of digitizing information is rarely used today, therefore the format is not supported by the operating system by default. You will need a special program - DjVu Reader.
The Portable Document Format (PDF) is a versatile file format that preserves the fonts, images, and layout of the original document, regardless of which of many platforms and which of many applications the document was created on. It was initiated by Adobe and was originally intended for electronic presentation of printed materials. PDFs look the same no matter what device they are viewed on. Whether you're using Windows 10, Mac, Chrome OS, Android, Windows Phone, iPad, or Windows XP - on any software or hardware, PDFs remain the same.