If I use Process.Start to open a file from a C # WinForms application, is there a way to control which monitor opens in PDF (or something else)?
Process.Start
You need to do two things: get the handle of the application window (for example, Acrobat Reader for PDF), then move it to the desired monitor and increase it.
These two articles will help you get started:
Managing the window state of other applications using C #:http://www.c-sharpcorner.com/UploadFile/gaurav.pilay/206232006095904AM/2.aspx
Multichannel programming in C #:http://www.codeproject.com/KB/cs/multi-monitor_in_c_.aspx