I have a shortcut icon I created that opens a viewer program I use.
If I highlight a document in Doupus, then click that program icon it opens that program with that document. Makes sense.
If I now highlight FIVE document names in Doupus, then click that program icon it opens five copies of program with one document in each.
Can I do this but have it load the 5 documents in one copy of that program?
(The viewer program itself does of course open multiple files when used independently)
Removing the @async: may do it, or may make it so each file doesn't open until the program has been closed after viewing the previous file.
Changing {filepath} to {allfilepath} may also do it, or may make it not work at all.
Or it may have other requirements.
If neither of those works, the program should come with documentation on how its command line works which can be used to work out what the command line it needs is. Getting Opus to then generate the correct command is usually pretty easy, once you know what it is.
You may have to look at the ViewMate.exe manual, or ask their authors/support/forum for the correct way to get their program to open more than one file at the same time.