Is a work free because it is online?

No. Free access is not the same as public domain status or a reuse licence.

Layered answer

Check each right separately

Being able to view or download a file says nothing by itself about permission to republish it.

A clear licence can permit reuse while copyright continues.

Public domain status depends on law and facts, not the file's price or location.

Sources

Commercial use?

Verify the exact material and intended country with qualified counsel.