Testing PDF files Codeception

Im using YII2, and Im starting to build tests using CODECEPTION. I tried looking for answers to this question online, but I could not find any.

What is the best way to test the genrated a generated PDF file for content. The scneario that I have is that we have generated reports that are sent by mail. Those mails will have attached PDF files that I want to test. I want to use functions such as

$I->see($text)

but for the generated PDF file.

How can this be done?