Sample code for 30+ languages & platforms
C#

SharePoint -- Update the Contents of a File (PUT)

Demonstrates how to update the contents of a SharePoint file.

Chilkat C# Downloads

C#
bool success = false;

//  This requires the Chilkat API to have been previously unlocked.
//  See Global Unlock Sample for sample code.

Chilkat.Http http = new Chilkat.Http();

//  If SharePoint Windows classic authentication is used, then set the 
//  Login, Password, LoginDomain, and NtlmAuth properties.
http.Login = "SHAREPOINT_USERNAME";
http.Password = "SHAREPOINT_PASSWORD";
http.LoginDomain = "SHAREPOINT_NTLM_DOMAIN";
http.NtlmAuth = true;

//  The more common case is to use SharePoint Online authentication (via the SPOIDCRL cookie).
//  If so, do not set Login, Password, LoginDomain, and NtlmAuth, and instead
//  establish the cookie as shown at SharePoint Online Authentication

//  Indicate that we want a JSON reply
http.Accept = "application/json;odata=verbose";

//  Update /Documents/ChilkatTest/sample.docx with new content...
Chilkat.HttpRequest req = new Chilkat.HttpRequest();
req.HttpVerb = "POST";
req.Path = "/_api/web/GetFileByServerRelativeUrl('/Documents/ChilkatTest/sample.docx')/$value";
//  Give the location of the file to be uploaded.  
//  Note: The file is not loaded into memory at this point.  It is never fully loaded
//  into memory.  Instead, the file data is streamed directly from the file when
//  when the upload occurs.
req.StreamBodyFromFile("qa_data/msword/sample.docx");

//  We need to add a form digest value in the X-RequestDigest header field.
//  See this example for details on
//  how to get (and cache) a form digest value
req.AddHeader("X-RequestDigest","SHAREPOINT_FORM_DIGEST");

//  Also need to add this header..
req.AddHeader("X-HTTP-Method","PUT");

//  Upload..
bool bUseTls = true;
Chilkat.HttpResponse resp = new Chilkat.HttpResponse();
success = http.HttpSReq("SHAREPOINT_HTTPS_DOMAIN",443,bUseTls,req,resp);
if (success == false) {
    Debug.WriteLine(http.LastErrorText);
    return;
}

//  A successful update will return a 204 status code with an empty body.
//  A non-successful update will return a JSON response body..
if (resp.StatusCode != 204) {
    Debug.WriteLine("Response status code = " + Convert.ToString(resp.StatusCode));
    Chilkat.JsonObject json = new Chilkat.JsonObject();
    json.Load(resp.BodyStr);
    json.EmitCompact = false;
    Debug.WriteLine(json.Emit());
    Debug.WriteLine("Failed");
    return;
}

Debug.WriteLine("Success.");