There exists a converter software available as part of Mathcad (Primo Converter) that should allow users to convert between various versions Mathcad documents (.mcd) and worksheets (.xmcd). Not all formats may be converted perfectly though and may require manual post processing by the user.
Convert PTC Mathcad worksheet to MathCAD document file.
We found one software available in the database for this conversion.
Microsoft Windows software - convert xmcd to mcd on Windows
A mathematical and engineering calculation software
Convert from xmcd file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.