This is most likely a case of not having added the "extension=php_mongo.dll" line to the correct INI file. You should be able to confirm the location of the INI file being used by your PHP runtime by reading the output of:
phpinfo(INFO_GENERAL);
...when executed from a script. The relevant line should read similar to:
Loaded Configuration File => /etc/php5/cli/php.ini
...although you'll no doubt have a Windows path. Additional INI files may be listed, too, for extra modules.
I'll also note that the
install docs you referenced link to our S3 bucket, which we were using to publish the DLLs until recently. The PECL website now provides builds of extensions for Windows, so you may want to download a newer version from
https://pecl.php.net/package/mongo, as the S3 bucket only has up to version 1.6.8. I'll try to get the install docs updated sometime this week, so we link directly to PECL.