Software architectural knowledge (AK) is the integrated representation of the software architecture (SA) of a software-intensive system, the architectural design decisions, and the external context/environment. AK annotation using AK conceptual model is used to recover formal AK from SA documentation, including architecture design as well as the design decisions, rationale, context, and other factors that together determine architecture solutions. But there is no evidence on how architects, especially junior architects, understand and annotate SA documents and recover formal AK from the documents using an AK model, which is right the case when a new architect jumps into a project, trying to understand the SA documents created by previous architects. This paper first presents AKRCM (AK Recovery using Conceptual Model) approach for recovering AK from SA documents. Second, we conduct a descriptive study using experiment to investigate how junior architects annotate SA documents and recover AK using AKRCM approach. We found that an AK conceptual model is beneficial for junior architects to get a fair understanding of SA documents, and to recover better-quality AK from SA documents.