What is the proper way to deal with a situation where a company (acme.com) is selling and implementing certain kinds of gadgets?
Each product has its own dedicated HTML product page, with only general information about the product. It also hosts data-sheets and vendor provided PDF documentation about the products linked from the product HTML pages. All together this is a setup that seems to be useful for real users.
Since these PDFs are mostly provided by the manufacturers, they appear in other places over the web, including rival websites. Many of these PDFs are detected as duplicate content by Google and the "Google-selected canonical" is the same PDF on someone else’s website!
Question 1: Does this mean that link-juice is leaked to those other random websites, even though acme.com is linking to the PDFs under it’s own domain?
Question 2: If answer to Q1 is yes, is adding
rel="nofollow" to those links pointing to the PDFs be recommended?
To make things more complicated when I check the Links section in Google Search Console, I can see that apparently acme.com have loads of External links, but when I take a closer look, many of those are pointing to identical copies of these PDFs mostly on another site. In other words Google makes it look like we have incoming external links, whereas in reality other websites has links to these duplicate PDFs on their own domain.
Question 3: Is it a bug in Google Search Console that it shows links to PDFs on other websites as incoming external links to acme.com?
Also when I look further I can find some of these PDFs, where the Google Selected Canonical seems to be the one on acme.com.
Question 4: Does that mean that with those PDFs acme.com is stealing link juice from other sites, even when they link to their own hosted version of the same PDFs?
Question 5: If Q4 is yes, does that mean acme.com should examine the PDFs one-by-one and add
rel="nofollow" (or prevent indexing in any other way according to Q2) to those links where the canonical is on another domain, but keep normal links to those PDFs, where acme.com has the canonical versions?
PS: I’ve tried to search for this topic for many days without finding even a mention of this kind of a situation. The closest I’ve found is this searchengineland.com article, but it is about only a slightly similar topic and it does not offer any solutions to the problem.