Hello,
sorry for the late reply. When you save in the PDF editor, PDF24 first converts the objects you added into PDF and then places them on the pages. The message "Could not convert file to PDF" means that this step failed. This step uses the Java runtime included in PDF24 Creator, and so did the conversion from PDF to Excel in your version.
Version 11.31.0 fixed memory errors of the Java based functions, which could occur especially on busy systems, and the conversion from PDF to Word, Excel and PowerPoint uses new converters since then. Please update to the current version 11.31.1 and try again.
If it still happens, please let us know your Windows version and how much memory (RAM) your computer has. So that we can reproduce this, please send us a file where it happens to forum@pdf24.org.
Until then, both functions are also available online: