PDF are text/images files
AVI is vide/audio files
You can't convert one to the other.
If you downloaded something that is supposed to be a Video, but for some reason has a PDF extension, just rename the file in a command prompt window to change the extension, for example to change file.pdf to file.avi you would have to type: rename file.pdf file.avi
Hope this helps, didn't really understand your question :/
AVI is vide/audio files
You can't convert one to the other.
If you downloaded something that is supposed to be a Video, but for some reason has a PDF extension, just rename the file in a command prompt window to change the extension, for example to change file.pdf to file.avi you would have to type: rename file.pdf file.avi
Hope this helps, didn't really understand your question :/