There could be several reasons why the file will not open:
1. your system has no .pdf viewer installed (like Adobe's Acrobat Reader), and you have the default .pdf reader in Chrome disabled: [
^].
2. the file name is incorrect.
3. the specific .pdf file is locked, encrypted, or you don't have permission necessary to open it.
For various techniques for displaying a .pdf in WinForms, see: [
^].