How can you add a rel canonical tag if you haven't created the wrong pages?

[Sika22]

For one of our white paper campaigns we are getting multiple URL's some how but we only have one version of the page.  So do I put the rel canonical tag on that one single page?  Will that fix the other url's from being indexed?  I'm assuming people are typing in the urls with underscores and capital or non-capital letters and it's showing up that way in analytics.  Thanks!

[ForForce]

Your question needs some clarification.

Is the White Paper in HTML or PDF format on your site?

Are you (or your client) the original author / owner of the white paper?  Is the White Paper exclusive to your site, or are there other places on the internet the white paper is available?

You say that you are not the 'creator' of the duplicate pages.  Are these duplicates on you or your clients site, or on external sites?

[SamuelScott]

Without seeing your site, I cannot tell you exactly. But here's the general best-practice:

1. Pick the one URL that will be the "main" one for that piece of content. Make it canonical in the HTML code of the page like this:

2. Then, put that exact same canonical tag (without any changes) in the code of any other page at any OTHER URL at which the content will be found. Google should then know that the original URL is the one to index and consider as the original one. For good measure, I'd also no-index the other URLs, just in case. (The canonical tag is only a suggestion, not a directive.)

Note: If people add underscores or change certain letters of a URL to capital letters, that should NOT take them to the same page as without underscores or with all lowercase letters. Any such changes are considered by Google to be completely-different URLs (and would most likely return a 404 "not found" as a result).

I hope that helps! Let me know if you have any questions.