Opening the file, an error indicates that the file cannot be opened. Even if I let LibreOffice repair the file, it won't open.
The Office documents such as .docx, .xlsx or .pptx file are compressed archives. By extracting those documents, you can retrieve the images, text and other embedded files.

Among the file extracted, the file document.xml is the file that contain the content of the file. Let's grep FCSC to see if we can find the flag.