Get PDF Page Count using Regular Expression

public int GetNoOfPagesPDF(string FileName)
{
int result = 0;
FileStream fs = new FileStream(FileName, FileMode.Open, FileAccess.Read);
StreamReader r = new StreamReader(fs);
string pdfText = r.ReadToEnd();
System.Text.RegularExpressions.Regex regx = new Regex(@"/Type\s*/Page[^s]");
System.Text.RegularExpressions.MatchCollection matches = regx.Matches(pdfText);
result = matches.Count;
return result;
}