Another reliable source is , which hosts a scanned version of the book. The file is available for free and in the public domain, but it is an older edition. You can find it by searching for "Orthographe Progressive Du Français" on the website.
The Ghost Lesson
If you’ve been learning French for a while, you know the struggle is real. You can speak, you can understand the gist of a conversation, but the moment you have to write — accents, accords, plurals, and the dreaded passé simple —everything falls apart. orthographe progressive du francais niveau intermediaire pdf