Attempting to download ASDM 7.18 without preparation will lead to frustration. You need three things:
While the UI remains consistent with previous iterations, version 7.18 introduces specific backend and security enhancements: cisco asdm 7.18 download
Do not download ASDM files from third-party "mirror" sites. These files control your network security and may be compromised with backdoors if obtained from unofficial sources. Attempting to download ASDM 7
Getting Started with Cisco ASDM 7.18: A Download and Installation Guide cisco asdm 7.18 download