Quote: Originally Posted by noap
I've found some tools on the internet, which are able to do that, but only if all the xlsx-files are in one folder. ...
That tool you linked to can handle multiple folders for the xls files but all of the converted files are placed in the same output folder. I didn't see any option to output the files to their original folder.
I assume you want the converted files to be outputted to their original folder?
It should be a trivial task for the developer to include the option to output the converted file to their original folder. You could try to contact the developer and ask if he would consider adding that option.
Here's one I found that can do command line processing: http://www.coolutils.com/Convert-XLS-XLSX
With command line ability, you could write a batch file that changes to each folder that contains files you need to convert, do the conversion, then change to the next folder. It would take some time to write the batch file but it should do what you want. Oops! Just realized that this tool doesn't support converting to xlsb, only converts to xlxs so it won't do the job.