Two suggestions - first, you can drag a QVD and drop it on the QV icon (or on the start page ifs open). This will create a new qvw file, and open the file load wizard with the preview window open, so you can see the fields and content. It you click cancel, no file will be created.
But this doesn't tell you much about metadata like cardinality. I have downloaded a QVD viewer in the past that did that. Search here for "QVD viewer" and you might be able to find it. This is a model that loads a sample (or all) of the date, and computes meta data for the QVD.
Hope this helps