The only doable pmd to xlsx conversion know to us, would be to save PlanMaker spreadsheets (.pmd) to one of the Excel formats (.xls, .xlsx). This appears to be only possible within the original software using the File ► Save as.. function.
Convert PlanMaker spreadsheet file to Microsoft Excel Open XML workbook and spreadsheet.
We found one software available in the database for this conversion.
Microsoft Windows software - convert pmd to xlsx on Windows
A handy spreadsheet editor from SoftMaker Office suite
Convert from pmd 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.