Read FileName+* from the folder

sneha

IF ISCLEAR(objShell) THEN
CREATE(objShell);
PrintThisFile := 'C:\Files\' + SO."No."+ '.pdf';
IF NOT EXISTS(PrintThisFile) THEN
ERROR(Text003,PrintThisFile);

SplitDirFile(PrintThisFile,Dir,FileName);
objFolder := objShell.NameSpace(Dir);
objFolderItems := objFolder.Items;
objFolderItem := objFolderItems.Item(FileName);
objFolderItem.InvokeVerb('OPEN');
objVerbs := objFolderItem.Verbs;
CurrForm.CLOSE;

I've the above code on Sales Order Screen to open the PDF file from C:\Files folder. But, the file name in the folder can be SO.'No."+yyy.pdf. Above code working only if I have the file in the folder with the name same as sales order number "No.".pdf. How can I open the file even if the file name contains sales order number+some more characters. How can I look for something "No."+*.pdf?