Upon running a conversion where you are appending the output to an existing file, you may encounter the error "Cannot append: file is read-only".
The first thing you should check is that all instances of Excel are closed, particularly the file you are attempting to append to.
If that's not the case, there could be a problem with your Office application or there is a security issue with the PDF you are trying to convert.
See if you can convert into a new Excel file. If that fails, attempt a conversion to .CSV. If you are not able to convert to Excel, but you can convert to .CSV, this points to the issue being with your Excel program and a reinstall may be necessary.
If none of the above appears to be the problem, we will need you to send us a copy of your PDF file so we can analyse it. Please send it to [email protected].