Short answer, "No." If your commercial textbook is still being sold by the publisher or is an older edition available for purchase through Amazon or other book sellers, it is not an Open Educational Resource. It's likely that the PDF (or other format) that you've found is a pirated copy that was posted illegally and is in violation of copyright. Federal investigators recently shut down one of these popular websites and have charged two Russian nationals with criminal copyright infringement, wire fraud, and money laundering for operating Z-Library.

While it is not illegal to share a link to a website or a link to an individual title hosted on the website, by doing so, you are infringing on the intellectual property rights of the author. These types of websites can also sometimes lead to sketchy downloads, which could impact less tech-savvy students by infecting their devices. It is also very likely that the PDF you've discovered is not accessible and because it was posted illegally, it could disappear at any time.

Downloading a PDF that you've found on one of these websites and then sharing it with students through Canvas is illegal and is a violation of copyright law unless you've gone through the proper channels to get copyright clearance from the publisher.

These scanned copies are also often not fully accessible, which means students who require a screen reader or other assistive device may not be able to use the resource.

These are just more reasons to consider adopting Open Educational Resources, which are legally free and provided under a Creative Commons license. The Zero Textbook Costs at CRC website is also a great place to explore OER and ZTC options for specific disciplines.