Upload PDF file (not required)

First, you need to check if the file was submitted before you do any validation. 

You can do so by using the [code]getFiles()[\code] function provided by CI. See documentation: Working with Uploaded Files — CodeIgniter 4.0.4 documentation

So your code would look like this:

PHP Code:

$uploaded_file = $this->request->getFiles('file');

if ( !empty($uploaded_file) ) 
{
    // File was uploaded, run other validation here
}
else 
{
    // No file was uploaded
}