It can be useful to have the same work in Commons in both PDF and DJVU. While DJVU files are better for transcription of the work to Wikisource, many ordinary users prefer PDFs as various PDF-readers are much more widespread than DJVU-readers.

However, if a DJVU file of a book is uploaded from the IA to Commons, the uploader does not enable to upload it again in PDF format, stating "A file named '[name of file]' already exists on Wikimedia Commons.

IA uploader should enable uploading the same book in both formats.