How could i check if the extract file from .gz is already in

Question

This Code should decomprees the .gz extention files and it does . but i want to check if the file is already extracted 
or the file is already exsosts .
How can I do that or check ? 
public static void Decomprees (FileInfo fileToDecompress)
{
 using (FileStream originalFileStream = fileToDecompress.OpenRead())
{
 string currentFileName = fileToDecompress.FullName;
 string newFileName = currentFileName.Remove(currentFileName.Length - fileToDecompress.Extension.Length);
 using (FileStream decompressedFileStream = File.Create(newFileName))
   {
    using (GZipStream decompressionStream = new GZipStream(originalFileStream, CompressionMode.Decompress))
    {
   decompressionStream.CopyTo(decompressedFileStream);
 }
 }
 }
  }