How do I transfer document and photo files from an external hard drive formerly connected to my old PC into my new iMac computer?
There are several different ways to move data from your old PC to your iMac, including Manually Migrating at > Switch 101: Migrate your Windows files or system to your Mac
If you just want to move file's from your External HD, simply plug it into your iMac and drag your doc's to your Documents Folder and Import your photos into iPhoto.
To Share data cross-platform using an External HD, see > Sharing drives - Macworld
Retrieving data ...