VB.NET Find if file with unknown elements exist?

I need to write an if function that finds if the a specific file exists, but the directory of the file contains unknown elements that may change from occasion to occasion. The code I have so far is:

If Dir(ProjectsFolder & ComboBox_ProjectType.Text & "\" & ProjectNumber & "\" & ProjectNumber & "_Rokasgramata\", ProjectNumber & "*User Manual*.pdf")(0) = "" Then

It returns an error and it's probably because of "*" What am I doing wrong? Could someone, please, help me with this one?