The linked post below should help.
Woked fine for me - I'm currently reading "The Book Thief" downloaded from Waterstones to Adobe Digital Editions on a mac and transferred from ADE to my Sony reader using the Finder.
Note that you 1st need to authorise the PRS-505 on a windows box using ADE.
Once the PRS-505 is authorised, you no longer need to use Windows (unless you do a hard reset, in which case you will probably need to re-activate the Sony using windows).
https://www.mobileread.com/forums/showthread.php?t=28883