All you need do is change the values on the matrix to % instead of references. To do this:
Open the matrix
In the 'view' Tab in the ribbon/toolbar click on the 'Node Matrix' option. In the menu that slides down, change the cell content from the default 'Coded References' to 'Column Percent' or 'Row Percent' as may be required.
If you wish to create a table showing how many words are in a source file, put the sources into both the row and column of a matrix and switch the cell content to display 'Words' as set out in the steps above. Each cell will ow display the word vount for each document. You can also export matrices to Excel if you need to do further calculations.
I hope this is helpful but do let me know if you need clarity on any of this 🙂