Hallo,
does DOs preview work when I install PDF-XChange Viewer and deinstall Adobe PDF-Reader?
If PDF-XChange Viewer provides an ActiveX viewer or Vista-style Preview handler then it should work. Why not try it and see 
As Jon says, try it and see.
I have recently messed around with a couple of viewer plugins. It started because I have paid for QuickView, which can handle more stuff than most and wanted to get it to work in DO.
My beginner's experiments have shown that you can tweak the way that DO works by turning viewers on and off, and by changing the order in which they do their thing.
For example, I recently found that I can get DO to change the way it handles mp3 files by going to the "viewer plugin" bit of preferences and turning off the addin in for mp3 format files. Doing that means that Windows media player kicks in instead. This is good if you want a volume control, but it also loses some other stuff.
Another recent experiment showed that changing the order of the plugins means that I can get the viewer to show mht files in all their formatted glory. If the plugins are in the wrong order, the viewer gags.
I go through all this to suggest that instead of installing the PDF-XChange Viewer and deinstalling Adobe PDF-Reader you just do the install and mess around with the viewer plugins. If the PDF-XChange Viewer shows up in the configuration zone for the Active X viewer and works, go ahead.
This strategy could give you a bit more confidence than the simple trial and error of uninstalling Adobe Reader. In the process, you might also get a handle on the complicated, but potentially useful, business of grappling with viewer plugins.
Yes it's terribly complex...
The sort order determines the plugin priority and the tick turns each plugin on and off. What were GPSoftware thinking when they designed such an opaque feature...
You underestimate, or play down, the complexity. More important, you do not seem to acknowledge that it is not always obvious where to find these settings, partly because the manual can't possibly hope to cover everything.
Unlike folks who don't need the manual, probably most of the people here, I have looked at it a lot recently. It cannot hope to deal with everything. It also gets a few things slightly wrong, or is at least misleading.
For example, the section on the "Viewer Plugin System" says "See the following section on the MP3 plugin for more information." Apart from wondering why there isn't a clickable link to that section – there is one now in my PDF file – you will not find the material in question by searching for "MP3 plugin". The bit in question actually appears in the bit describing "MP3 tag editor".
No big deal, but enough to make it worth passing things on to someone who may just be at the foot of the learning curve.
I forgot to mention first time around that in my configuration at least, there is a quicker way to get the viewer plugin than the one mentioned in the manual, thank to the separate menu entry >>Settings>>Viewer Plugins. But everybody knew that anyway.
And your advice to the person who asked the question is?
Jon already gave the only advice that was needed: It will probably work, so try it and see.
If the PDF-XChange Viewer is intended as an alternative to Acrobat Reader then it will probably install itself as the PDF viewer for Internet Explorer and thus work in Opus via the ActiveX plugin without any further thought or configuration.
...In fact, a quick search of the forums for PDF XChange reveals that someone already posted a thread mentioning the program and saying it definitely does work with Opus so there's no need to complicate things further or speculate. It works. 
Re the manual, yeah it would make sense for the plugin names to be clickable links (where there is further information for the plugins in the manual), so mention that to Greg if you want to see it. However, the plugins are described in the next pages/sections of the manual so if you have the table of contents open, or just scroll down, it's not hard to find them.
It works for me here - no problems. I don't have acrobat installed at all, and can preview and open pdfs without a hitch using pdf-Xchange viewer.
I do have Acrobat installed and it is a pig. Unfortunately, it is the only way to create PDF files with all of the bells and whistles in the way of active internal hyperlinks. Guess that's why it is the way they create the DOpus Help file.
Acrobat is, though, horrible as a reader. And Adobe Reader isn't much better. Free Foxit does not allow annotation, and, as someone has pointed elsewhere, it doesn't always "thumnbnail". So it was interesting to read of an alternative.
Unfortunately, when I first tried to find the docu-track site this morning, it was down. It seems to be there now, but only just. Try to download from it and I get a "link seems to be broken" message and an invitation to shell out some money through PayPal to get the thing.
Eventually I found it on Downoad.com.
But that seems to be an old version, according to Snapfiles, which points you at docu-track.
PCWorld seems to have its own version.
It doesn't work for me!
When I want to preview a file, the whole program opens.
Presumably it does the same thing in Internet Explorer? There may be an option within PDF-XChange which tells it whether to open within browsers or to open its own windows. There is with Acrobat Reader, at least.
Any idea what to do, Leo?
Yeah, see if it does the same thing in IE and if it does look for an option to tell it not to.
I got it! Perfect! Thanks!