Uploadfile format check

Code
Public   Bool Canupload ( String Filename)
{
If ( String . Isnullorempty (filename ))
{
Lblmsg. Text =   " Please select files! " ;
Return   False ;
}
If (Filename. indexof ( " ' " ) >   - 1 )
{
Lblmsg. Text =   " File Name shocould exclud qotation marks! " ;
Return   False ;
}
If (Filename. indexof ( " . " ) =   - 1 )
{
Lblmsg. Text =   " Unrecognizable file! " ;
Return   False ;
}
Int Contentsize = Fileupload. postedfile. contentlength;
If (Contentsize >   4470784 )
{
Lblmsg. Text =   " File size is larger than 4 MB! " ;
Return   False ;
}
If (Contentsize =   0 )
{
Lblmsg. Text =   " File size is 0! " ;
Return   False ;
}

// Attachment type does not allow upload
String Filetype = Filename. substring (filename. lastindexof ( " . " ) +   1 ). Toupper ();
Bool Canuploadfiletype =   False ;
// Allowed types of Upper Limit
String [] Canfilestype =   New   String [] { " JPG " , " JPEG " , " PNG " , " PDF " , " PPT " , " Txt " , " Xls " , " Doc " };
For ( Int I =   0 ; I < Canfilestype. length; I ++ )
{
If (Canfilestype [I] = Filetype)
{
Canuploadfiletype =   True ;
}
}
If (Canuploadfiletype =   False )
{
Lblmsg. Text =   " Unacceptable file! " ;
Return   False ;
}
Return   True ;
}