I just got a Mobi ebook from a friend, and converted it to azw3. But on the Kindle there was just absolute gibberish on screen with weird characters etc.
Does this conversion not usually work?
If the source book is OK, the conversion should be good. Does it look right when viewed in calibre?
Have a look at the KF8 eBook in the Calibre editor and see what's there.
if all else fails, use the kindle unpack plagin to get at what's really in the mobi. if its print replica, that plug in will extract a pdf
That's also a good idea.
I don't really understand these answers at all, thanks for trying to help though
Perhaps your friend's book was encumbered with DRM?
Both azw3 and mobi look fine on my kindle. On hers the azw3 was just gibberish but the mobi I made from the azw3 was fine. There was no drm on the book.
I just realised I made a massive booboo I am sorry.

So I had an azw3 file. It worked perfectly on my Kindle. I sent it to my friend so she could read it too, but it was just gibberish on her screen. So in Calibre I converted it to mobi which was also perfect on my Kindle. And when I sent it to her the mobi version viewed perfectly on hers too.
So I am confused why the original azw3 file viewed perfectly on my Kindle but not hers?
The only reason I ask is that sometimes when I convert to Mobi the conversion is bad so I prefer to stick with azw3 if I can.
On mine yes, both are perfect
But it wouldn't convert if it had DRM.