Import and transpose

> I have an existing sheet music score for a viola which I like to transpose to a flute score.
> I followed all your tutorials however could not find a topic for importing existing scores
> I tried the following:
> I scanned the viola part using Windows 7 and saved the scan in a.pdf format.
> Next ,in Musescore - File - New - clicked on "Plugins" selected "import ABC" I loaded my saved .PDF file into Musescore.
> Here I need your assist,Musescore apparently requires a format other than.pdf.
>
> What conversion software do I need to satisfy the Musescore setup?
> Please direct me to a tutorial/handbook that describes the transposition scenario on imported scores.
> Thanks very much.
>