Just a note for those facing similar problems with any of the MS Office "emulators." You may find you encounter issues with documents created with the latest versions of MS Office applications on PC's, i.e. .docx or .xlsx files. (May affect PowerPoint files, too. I'm not sure.) All of these emulators tend to be a version or so "behind" Microsoft's most recent versions and you'll need to either convert the files (as noted above) or create the files in a form compatible with earlier versions of MS Office.
Another problem may arise if you are trying to deal with a file that was created by an MS Office "lookalike" such as Open Office on a PC. I've found that such files appear to be true MS Office files (i.e. they have an appropriate extension such as .xls) but will not open with an emulator such as Documents To Go. The workaround is to open such a file with the true Microsoft program (e.g. Excel) on a PC and then save it. Once saved, it can then be transferred to a device running the emulator. BTW, my experience is with Documents to Go on this point but I suspect other MS Office emulators may suffer from the same problem.