It sounds like you want to know how to change permissions so the file can be edited elsewhere. Right click on the file and select Get Info. At the bottom there will be a Sharing and Permissions Section. Under the Name everyone, toggle to read and write.
Alternatively, you may be able to open the file on the PC and create a new copy of the document using the save as command. You should be able to edit the new copy.
Of course you need to save or export the file to a format that can be opened and edited by windows software in the first place.