These files are frequently password-protected. If the "post" you were looking for was meant to provide a password, common defaults often include the name of the website/channel where you found it (e.g., @channelname ).
You will need the 7-Zip software to extract it. A1 DDN.7z
Once installed, right-click the file and select "7-Zip > Extract Here" or "Extract to A1 DDN/" . These files are frequently password-protected
It is common for community-made patches or "All-in-One" (A1) updates to be distributed as compressed archives. How to Use the File A1 DDN.7z
If you have downloaded this file and need to access its contents: