Sort of. Not all journals are peer reviewed and not all documents within a peer reviewed journal are peer reviewed.
If an article is well cited then it's likely to be from a peer reviewed journal and it's likely to be a peer reviewed article. In any case, that document has academic relevance which has probably gone through a peer review-like process such as the publication of a textbook.
The way you can tell is if the journal is peer reviewed is if it says its peer reviewed and the peer review process is provided on the website where authors submit articles.