Are you saying the links fail when you test? Or are you just seeing the %20 and making the assumption they will fail?
It's quite possible that the links will work just fine as most browsers I believe will correctly interpret the %20. But on the outside chance this doesn't work, you can always just rename the PDF so as to either substitute an underscore for the space as in My_File.pdf, or you could collapse the spaces and use CamelCase as in MyFile.pdf.
The links fail when I test them. I am using Firefox. Since I don’t own the PDFs, I’m looking for a solution without renaming the PDFs.
Well, it's not really what I would call "Elegant", but this might help you achieve the goal.
You might consider using an HTML page outfitted with a meta redirect. Essentially, you would create this html page just as you would any other topic. But you would then just copy the code and delete the topic. Then use Windows Notepad to re-create the topic. Then amend it with the redirect code. Then add this topic as a Baggage File.
My thought here is that by adding it to baggage, RoboHelp won't be tempted to "help you out" by filling in %20 where the spaces were.
You can certainly try just amending the topic inside RoboHelp with the meta redirect as a first step. It's entirely possible that RoboHelp will ignore the spaces in this case. Then if that fails, try the steps I mentioned earlier.
The meta code can be placed anywhere inside the HEAD area of the topic. And it would look like this:
<meta http-equiv="refresh" content="0; url=Path and File Name.pdf" />
Give that a try and see how it works.
I didn't have to add the file as a baggage file - but the meta code in the HEAD area worked for me.