How can i use MTOM encoding to return pdf in WCF

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WCF

Here is my requirement
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I need to create a WCF service, It should get User Name and Password of request as an input and it should return the pdf file as an response (it must be a binary file).
Here the file size might exceeds 5 MB, So i don't want to see any delay in response of WCF service

Please share us any idea or code for the given requirement

Your response is highly appreciated.

please respond me ASAP