You're looking for an interesting feature to make your C1-level international Spanish course PDF materials more engaging. Here are a few ideas:
Mastering Advanced Spanish: Why Aula Internacional C1 PDF is the Better Choice for Learners aula internacional c1 pdf better
While the Aula Internacional C1 PDF is a great resource, there are other alternatives that learners may find useful: You're looking for an interesting feature to make
Since I cannot modify a real PDF directly, I am providing a product/feature specification that you (or a developer/tutor) could implement using PDF editing tools (like Adobe Acrobat Pro), note-taking apps (Like GoodNotes/Notability), or a custom web wrapper. You must stop doing this
The biggest trap of the C1 book is the "Passive Agreement Trap." You read a text, understand it, nod, and move on. You must stop doing this.