Is it possible, writing to excel file which is in client's computer, need help

Hi everyone;

Is it possible to write to a excel file which is in the client's computer, from server side? Let me explain... Think of there is a file in 'c:\sample.xls' . I want to reach at it and write my values to it. Is it possible? 

And if it's not possible;

Is there any way that writing to a excel file that is in my project on server. In this scenerio I want to reach at the file that is in the path of 'ftp://xxxxxxxxxxxxx/documents/yyy.xls and write to it.

I need help.Thank you;
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