Canonical tag is necessary where the 1 content is matching with another one. If you are having 400 words content on your xyz page and the same content you are pasting on another page then Search Engine will count that content as the duplicate content. You must not do that, it will harm your search engine growth. If you want to avoid duplication issue then use Canonical Tag or rewrite it.
Yes, it will make also duplicate content issue if you are having pdf version for similar content. Search Engines read pdf files but we can not use canonical tag in pdf files.
Post edited by TechnoBear to remove promotion and fake signature