A PAC file is a Proxy Auto-Configuration file that contains a JavaScript function that determines whether web browser requests go directly to the destination or are forwarded to a web proxy server. A PAC file allows the client desktop browsers to be configured to select when to connect direct or when to use the proxy based on the URL and the host name. A PAC file can be downloaded from a web server or a local file. A PAC file is more suitable for complex proxy configurations or multiple proxy servers12

A transparent mode is a proxy configuration where the client browsers do not need to be configured to use the proxy. The proxy intercepts the traffic and forwards it to the destination. A transparent mode does not allow the client browsers to select when to connect direct or when to use the proxy34

A forward file is not a valid proxy configuration method.

A bridge mode is a network configuration where a device connects two or more network segments and forwards traffic between them. A bridge mode is not a proxy configuration method5 References := 1: Proxy Auto-Configuration (PAC) file - HTTP | MDN 2: Proxy auto-config - Wikipedia 3: Explicit and Transparent Proxy - techdocs.broadcom.com 4: Configure Explicit Proxy - Palo Alto Networks | TechDocs 5: config web-proxy explicit | FortiGate / FortiOS 7.4.0