This is a very good question.
When you select the LAUNCH Action, you are given an opportunity to Browse for the file you want launched -- say a PDF or DOC file. OPUS then enters the entire path name (eg C:\MyDocuments\Project1\filename.pdf). In Preview mode it will work, BUT when you Publish to a CD-ROM and run it on another computer it won't because they don't have that file in that location on their computer. Does that make sense?Solution:
Here's how to solve the problem. First, wherever you are Saving your OPUS imp file, also place a copy of the file you want to Launch in the same sub-folder. This will allow the Launch to work in Preview mode. Second, after you use the Browse feature to locate that file, manually remove everything but the file's name and extention (eg "C:\MyDocuments\Project1\filename.pdf" becomes simply "filename.pdf"). Finally, when you create your CD-ROM, manually place this file (filename.pdf) into the directory along with your Publication .exe file.
OPUS first looks for files you want to Launch in the directory where the imp or exe file is located. Yes, you can make this more complicated by initially telling OPUS the file is "\Project1\filename.pdf" but then you've got to create a sub-folder on your CD-ROM with the same location.
You can also use the OPUS system Variable called "<SYSTEM_PUBLICATION_DIR>" as the location of your file, but I've found my initial solution works without having to use it.