how can I get all the files in a local directory in c#

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C#

ASP.NET

Hi,
I am using MVC4 and VS2013. My doubt is I need to get all the files in a directory that is I don't want a normal file upload. So I am using
string[] getACHfilefromroot = Directory.GetFiles(directoryach); where the directoryach has the root/path and it is returning as string array not as files.

But I need to process these files and then I want to use InputStream that is
streamUsaePay = fileusa.InputStream; is the code which is used with in a foreach loop inside another Action Method and fileusa is the var that holds filename extracted from getACHfilefromroot.
And the thing is I need to process the .csv files or xlsx files and then need to split the details into 4 t o 5 txt files by clustering it.

Why I am stressing that I need to use InputStream is I am passing that stream variable for further processing.

I am trying different logics for hardly two days to get the files as stream/as files itself but I am not.
Please can anyone help me?
Thanks in Advance!!