Please refer : Opening PDF from a folder fails - #4 by ClaytonM
If item is the file in a ForEach that you want to pass in the argument field, then you can do it like this:
""""+item.ToString+""""
The 4 quotes on the ends should embed a quotation mark on both sides of the file. You can also verify this with a message box or write line and check if the filename is correct.
Regards.