Is there a way to link to a certain page/paragraph in a PDF document in Canvas?
I'm not sure if there is a way to do it with files uploaded to Canvas because of the way they handle the download URLs.
I do have a workaround for you though. If you upload the file to Dropbox (or host it on a personal domain) then you can just add the designation #page=8 to the end of the URL to go to particular page number. You can also use the #NamedDestination tag to go to a particular paragraph if the PDF has a "Named Destination" associated with that paragraph.
Here is an example of a PDF that will open on page 2 that is hosted through my Dropbox account:
Not a direct answer to your question, but just a consideration: if you can get the content out of a PDF and into a Canvas page it is far more accessible and infinitely more mobile friendly than a PDF is. Obviously this isn't a good option for forms or scanned articles and the like, but something to consider if avoiding a PDF is an option, you definitely get benefits from using Canvas pages! :-)
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