Websites like NHTSA.gov (for US models, though the Avanza is rare there) or similar regional safety boards often host "Technical Service Bulletins" (TSBs). While not a full manual, these PDFs cover common issues and fixes.
If you want a permanent, clean PDF without a subscription:
You search "toyota avanza service manual pdf download best" on Google and find a site promising a "Free 500MB file." You click download. Here is how to identify a scam:
Most mechanics guess. The service manual gives you the exact sequence for the DOHC engine. You learn that the exhaust valves tighten over time. With the manual, you use a feeler gauge and a 10mm wrench to restore lost horsepower in 90 minutes.
Toyota has an official portal (techinfo.toyota.com). While this is not a "free download," it is the legitimate source. You can purchase a subscription (usually for 1 day, 1 month, or 1 year) and download all the technical PDFs for your specific VIN.