These are keys shared on forums or "key-gen" sites. Because they have been used thousands of times, Microsoft’s activation servers often flag and block them.
Office 2007 uses a 25-character alphanumeric code. During installation, the software asks for this key to verify your license. While some keys might allow the installation to finish, the software may still attempt to "phone home" to Microsoft to verify the ID. If the key is blacklisted, you will be stuck in "Reduced Functionality Mode," where you can view documents but cannot edit or save them. Are There Modern Alternatives? microsoft office 2007 product key 100 working link
If you still have your original Office 2007 disc case, the working product key is usually located on a bright orange sticker on the back of the CD case or the manual. These are keys shared on forums or "key-gen" sites
Many sites claiming to offer "activators" or "cracks" are fronts for malware, spyware, or ransomware. How Activation Works for Office 2007 During installation, the software asks for this key