Patent systems rely on information infrastructures that enable searchers, examiners, and other specialists not only to consider legal requirements but also to gather market intelligence, competitor analysis, and other strategic business information. These resources are today considered fundamental to the assessment of a patent system's performance in terms of its reliability and legitimacy. However, this potential was constrained historically by the multiplicity of formats, languages, and time frames in which patents in different jurisdictions were published and issued. This essay traces how a secondary market for patent information materialised from a distinct commercial engagement with these peculiarities of patents as documents. In doing so, the essay explores how patent literature was abstracted, centralised, and filtered through private information providers such as Derwent Publications Ltd that began offering customised patent information products and services in the post-war decades.