An illustration of how to manipulate the metadata or data used to generate the PDF.

function redcap_email($to, $from, $subject, $message, $cc, $bcc, $fromName, $attachments)
{
    // You may want to send out emails via an alternative method or configuration,
    // OR maybe change something in a particular email based on some decision logic.

    // If this hook function returns FALSE or 0, that will prevent REDCap's email function from sending the email using the normal method.
    // If anything other than FALSE or 0 is returned (including not returning anything), REDCap will proceed with sending the email as usual.
    return TRUE;
}

A much more manageable way to perform project-specific operations for many projects at once is to create a directory structure where each project has its own subdirectory under the main Hooks directory (e.g., named "redcap/hooks/pid{$project_id}/redcap_survey_page.php"). This allows the code for each project to be sandboxed and separated and also makes it more manageable to utilize other files (e.g., PHP, HTML, CSS, and/or JavaScript files) that you can keep in the project's subdirectory (i.e., "pid{$project_id}") in the Hooks folder. Then the designated project handler PHP script can utilize any of the parameters passed in the function to perform actions specific to each project. NOTE: This example assumes that the "hooks" sub-directory is located in the same directory as the PHP file containing the Hook functions.

function redcap_email($to, $from, $subject, $message, $cc, $bcc, $fromName, $attachments)
{
    // Use the email values passed into this hook function to send an email using an alternative configuration.
    // If the sender's address is a Gmail address, then use Gmail SMTP server to send it instead of using our SMTP server defined in PHP.INI.
    if (stristr($from, '@gmail.com') !== false) {
        // Use Gmail SMTP configuration, etc.

        // Return false to prevent REDCap from sending out the email a second time
        return FALSE;
    }
    return TRUE;
}