Yes, Gramática Ativa 1 is essential. And yes, you can find a free PDF if you look hard enough. But the time you waste searching shady websites is time you could spend actually learning Portuguese.
It typically includes a "Key to Exercises," making it a powerful tool for self-correction. Why Students Search for the PDF
If you have the PDF, print the exercise page. If you cannot print, write your answers in a notebook. Typing over a PDF doesn't stick in your memory.
Gramática Ativa 1 PDF: Is It Legal? Plus Free Alternatives & How to Use It Effectively