How can i get the Directory.GetFiles to only show me files starting with a numeric value (eg. 1abc.pdf);
Directory.GetFiles(@"C:/mydir", "0-9*.pdf")
To get files that start with any numeric value, regardless of the number of digits, you could use a regular expression:
var files = Directory.GetFiles(@"c:\mydir", "*.pdf")
.Where(file => Regex.IsMatch(Path.GetFileName(file), "^[0-9]+"));
//.ToArray() <-add if you want a string array instead of IEnumerable