“ DjVu DjVu files are an open source container format, holding page images and text to replicate scanned documents. As an open format from the start, it was allowed to be hosted on, and supported by, Wikimedia. DjVu has been supported since the beginning of the ProofreadPage extension and held a monopoly regarding proofreading on Wikisource for a long time. This head-start is part of why DjVus are still the most popular format on the project.
Advantages Compatible philosophy: The DjVu format is and always has been an open format, while PDF was originally a proprietary format owned by Adobe. ”

“ For the most part, this is not a problem for proofreading as long as text is legible. It can be a problem with smaller text or text on the borderline of legibility. This might be a problem for illustrations and other images, if the images are being extracted from the file. ”

“ Nevertheless, it can be easier to work with smaller files because various processes (extracting images etc.) are quicker. Tried and tested: DjVus have been in use on Wikisource for longer than PDFs. It is more likely that any problems that can occur have already occurred and have been solved. DjVu files are less likely to cause problems with the ProofreadPage Extension or Wikisource in general. Disadvantages Lower resolution: DjVu files have a lower resolution than PDFs. ”