If you downloaded this from a student forum or a "referati" site:
Upload the .rar file to VirusTotal before extracting. If you downloaded this from a student forum
These files often require a password mentioned in the original forum post where you found the link. To help you better, could you tell me: If you downloaded this from a student forum
The use of a .rar wrapper for a single .pdf is often done to: If you downloaded this from a student forum
Ensure the site has a good reputation among peers.
Be extremely cautious if the file inside is actually named material.pdf.exe . This is a common tactic to hide malware. Always ensure the final extension after extraction is truly .pdf .