So I only researched this problem under Perl, forgetting that you have to hunt around under VB to find answers like this. Turns out it is possible, and easier than I imagined.
#!/usr/bin/perl -w
use Win32::OLE;
use Win32::OLE::Const;
my $wd = Win32::OLE::Const->Load("Microsoft Word 14.0 Object Library")
+;
my $word = Win32::OLE->GetActiveObject('Word.Application')
|| Win32::OLE->new('Word.Application','Quit')
or die Win32::OLE->LastError();
$word->{Visible} = 1;
$filename = 'foobar.doc';
$pw = 'foobar';
$savename = 'foobarsave.doc';
my $doc = $word->Documents->Open($docname)
or die Win32::OLE->LastError();
$doc->SaveAs( { FileName => $savename, Password => $pw});
$doc->close;
$word->close;
However, there are some hitches. There is apparently no way to just save the same file with a password, or if there is I couldn't find it. If you execute the SaveAs statement above with the same filename nothing happens--i.e. there is no error, nothing gets saved, and no password is added. You have to save it with a different name like I did in the example code. It might work if you changed the file in some way, like adding a space at the end, but I didn't try this.
