You can find something about this in the Adobe Developer FAQ. (It's a PDF document rather than a web page, which I guess is unsurprising in this particular case.)
The FAQ notes that the use of the command line switches is unsupported.
To open a file it's:
AcroRd32.exe <filename>
The following switches are available:
/n
- Launch a new instance of Reader ever if one is already open
/s
- Don't show the splash screen
/o
- Don't show the open file dialog
/h
- Open as a minimized window
- /
p <filename>
- Open and go straight to the print dialog
- /
t <filename> <printername> <drivername> <portname>
- Print the file the specified printer.