Rename files to avoid overwritten ones already saved http://blog.tiagosalgado.com/2013/01/08/replace-filenames-to-avoid-overwrite-the-ones-already-saved

gistfile1.cs

private List<CustomFile> fileList;

void Main()
{
  fileList = LoadFiles();
  var filesToAdd = new List<CustomFile>() {
		new CustomFile { FileName = "file.txt", owner = @"domain\user" },
		new CustomFile { FileName = "file1", owner = @"domain\user" },
		new CustomFile { FileName = "file.txt", owner = @"domain\user" }
	};
	
	foreach(var file in filesToAdd)
	{
		SaveFile(file);
	}
}

public void SaveFile(CustomFile file)
{
	// presist the original filename
	var originalFileName = System.IO.Path.GetFileNameWithoutExtension(file.FileName);
	// get number of files with same name
   var count = fileList.Where(j => j.FileName == file.FileName).Count();
	var appendCount = 1;
	
	while(count > 0)
	{
		var fileExtension = System.IO.Path.GetExtension(file.FileName);
		file.FileName = string.Format("{0} ({1}){2}", originalFileName, appendCount, fileExtension);
		appendCount++;
		// check again
		count = fileList.Where(j => j.FileName == file.FileName).Count();
	}
	
	// add to files temporarily just to ensure that when we upload multiple files with same that, the rename function will be executed correctly
   fileList.Add(file);
}


public List<CustomFile> LoadFiles()
{
	return new List<CustomFile>() {
		new CustomFile { FileName = "file.txt", owner = @"domain\user" },
		new CustomFile { FileName = "file (1).txt", owner = @"domain\user" },
		new CustomFile { FileName = "other file.txt", owner = @"domain\user" }
	};
}

// dummy class for file but we don't really need this
public class CustomFile
{
	public string FileName {get; set;}
	public string owner {get; set;}
}