Packaging Corp. of America (NYSE: PKG) is set to release third-quarter 2018 earnings on Oct. 24 after the close of trading. Shares of the packaging manufacturer have slumped 28% year to date as investors have fretted over the company's ability to sustain profit margins. Let's preview Packaging Corp.'s earnings report to understand why investors are concerned and to see if the upcoming filing can initiate a rebound in the company's stock.Image source: Getty Images.Packaging Corp.