Q: I cannot open any files transferred from the PC to my MAC as I am "not authorized". How can I correct this?

Select the folderr containing all of those files, CMD+I, click on the lock, enter your admin password, add yourself with read & write, and click on the action button and select apply to enclosed items. That should do the trick. BTW, I don't have a PC, so i've not transfered any such files to my machine.