How to open pdf in Android with external app?

Hi all! I need to open a pdf file with my Unity App in Android with a pdf reader installed on my phone. I have put the pdf inside Assets folder of my project and in Unity project preview all works very well, but when I try the app on my android's phone i get an error and the file could not be opened. I am using this C# code:

 Application.OpenURL ((Application.dataPath) + "/nameofmyfile.pdf");

Thanks in advance for the help!