How to get client machine access from Server ?

Hi,
how can i access client machine's specific file contained in a drive or folder.Suppose in Server side i have knowledge of full path of a file that is present in client side,  like "D:\ABCFolder\xyzFile.doc", this is a file that i want to retrieve and store in server side .
Can you tell me how can i access any file in client's machine through code ?
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