I tested your scenario/case using your sample PowerPoint presentation. I used latest version of Aspose.Slides for Java v23.10 and it works fine. The output PDF is fine tuned and the space interval is same with PPTX file. Please find attached the output PDF for your reference. EPPR_70126.pdf (96.7 KB)
I found you are using an older version of the API, so you have found this issue/behavior. We recommend you kindly try using latest version of the API and it will resolve your issue.
Let us know if you still have any issue when using latest version of Aspose.Slides for Java.