You don't even need Perl for this, as long as the printer is the default printer. If you right-click on a .pdf file, you will notice that there is a context menu entry labeled 'print'. Looking for the corresponding action with Regedit.exe, you will find some special invocation of acrord32.exe using the /p command line switch (or so I think I remember). Use system() with that switch to make Acrobat Reader print the .pdf.

For the second part of your problem, setting the default printer temporarily to something different, look at what Win32::Printer has to offer, together with Win32::Printer::Enum.