We examine teachers' use of resources as they prepare to teach the topic of numerical series of real numbers, in order to identify how their "personal relationship" with mathematical content--and its teaching--interacts with their use of a commonly used textbook. We describe this interplay between textbook and personal relationship, a term coined in the Anthropological Theory of the Didactic (ATD, Chevallard, 2003), in terms of "documentation work" ("resources," "aims," "rules of action," "operational invariants"), a key construct from the documentational approach (DA, Gueudet & Trouche, in "Educational Studies in Mathematics," 71, 199-218, 2009). We do so in the case of five post-secondary teachers who use the same textbook as a main resource for teaching the topic. Documentational analysis of interviews with the teachers led to the identification of their aims and rules of action (the "what" and "how" of their resource use as they organise their teaching of the topic) as well as the operational invariants (the "why" for this organisation of their teaching). We describe the teachers' documentation work in two sets of aims/rules of action: scaffolding mathematical content (series as a stepping stone to learning about Taylor polynomials and Maclaurin series), and organising student learning about series through drill exercises, visualisation, examples, and applications. Our bridging (networking) of theoretical constructs originating in one theoretical framework (personal relationship, ATD) with the constructs of a different, yet compatible, framework (documentation work, DA) aims to enrich the latter (teachers' documentation work) with the individual agency (teachers' personal relationships with the topic) provided by the former.