I would consider the Watchmen Comic’s as primary text/canon because they were made by Alan Moore, the creator of this universe and its stories and characters. While the Watchmen movie is an adaptation that takes the comics and places them into a new medium, film. Accordingly, the Watchmen film attempts to follow the comics in a film format, thus not creating anything significant or new, but retelling the same story. Thus, it can only be considered adaptation and not fanfiction.
On the contrary, the Watchmen show cannot be considered an adaptation because it is a new revision of the Watchmen series that brings new stories along with some iconic character appearances. Overall, this show does not try to tell the same story as the comics, but takes a new approach. Although, based on research, Alan Moore wants nothing to do with the Watchmen series. For this matter, I believe it cannot truly be considered canon or primary text because the creator and owner of its universe does not endorse its stories. Additionally, it is hard then to not claim the TV series a fanfiction, but it was ultimately made for profit – thus clouding this term. Alternatively, it is not truly an adaptation because of the new stories it brings and the changes it has made in the world, along with it not following Moore’s comics. Because of this, the TV show series is some combination of an adaptation and fanfiction.