Digication is a primary method to submit assignments in your course. Assignments are also where you can look for feedback.
Adobe Reader DC has numerous tools for annotating PDFs.
You can add marks to insert, replace, and delete text. Click headings below to display details; click again to collapse.
Adobe Reader lets you mark up PDFs easily. After you add a highlight, you can insert comments about it.
Adobe Reader is a free app available for a wide variety of computers and other devices.