If you google your intention of converting djvu to pdf, all you get are those online conversion sites?! Just install and use djvulibre to convert. More precisely like this:

ddjvu -format=pdf file.djvu file.pdf

I cannot use DJViewer app, as it is unsigned??? The djvulibre package from brew gave me some other new binaries to play with in addition to ddjvu short for decode djvu. Probably will never need them.