Hi namojainashis...,
First save the doc to folder and then read the bytes from file path and assign to th method.
Refer below code.
string xml = App_Code.Common.AddDocInputXml(insertid, ObjDoc);
string XMLfilename = Id + "_" + ddlDocType.SelectedItem.Text + "_" + txtVersion.Text.Trim();
xmldocument xdoc = new xmldocument();
xdoc.Loadxml(xml);
xdoc.Save(Server.MapPath("~/Document.xml"));
byte[] fileBytes = File.ReadAllBytes(Server.MapPath("~/Document.xml"));
UploadToFTP(ftp, userName, password, ftpFolderXML, XMLfilename + ".xml", fileBytes);