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I actually like it - think it makes sense for what you're describing, and I don't think I'd change it. The other option might be a 301 redirect or simply linking to only one site, but then you'd be changing branding/domain and possibly losing the customer.

We simply have the .pdfs on our own site and many people link to them.  We are happy to have those links and those links make these .pdf documents rank in the SERPs for important keywords (you can edit the properties of a .pdf document to produce a "title tag" that will optimized them and display in the SERPs.). We could add a notation to our website that invites people to post them on their own website or add customized branding (still keeping the embedded links to our own site).   Or, we could contact webmasters who link to them on our site and offer the custom brand if they host the document on their own server.  That would get us some additional backlinks.

Right, I understand all of that, but it doesn't really answer the question.  My question is regarding anchor text that INCLUDES the keyword vs anchor text that is ONLY the keyword.  So is it OK to have a high percentage of anchor text that includes the keyword (based on numbers in OSE's anchor text "terms" instead of "phrases")?