The PDF Reader trial does not have any restrictions on how you use the app. In addition to the PDF editing tools, this trial version includes the ability to recognize text content via the OCR converter, and convert files to and from PDFs as well.
Once your trial has expired, you will still be able to use PDF Reader for free with the basic features of PDF viewer and annotator.
You will need to purchase a license to continue using PDF Reader if you want to continue using the advanced tools. Depending on your needs, you may choose to upgrade to either the Standard or the Pro version.
The trial to in-app purchase/subscription on the App Store is slightly different. Please take a look at the article for more details.