Assuming you installed The Uniform Server Installed.
1. Navigate to \core\php54\extensions and verify php_ldap.dll is there.
2. Open \core\php54\php_development.ini or php_production.ini depending on which one you are using.
3. Find ";extension=php_ldap.dll" and remove the semi-colon so it should read "extension=php_ldap.dll"
4. Save and Close.
5. Stop and Restart Apache
6. View your php_info() to make sure the ldap section is there