The correct answer is B. Flex prompt templates are designed for custom input patterns, and Salesforce Prompt Builder allows specialists to define resources for the template. When the business wants to add a PDF as another input, the right declarative action is to add a file input/resource in the prompt template configuration, then use that resource in the prompt body. Option A is wrong because reindexing is a retrieval/search-index activity, not the standard way to add an input resource to a Flex template. Option C is wasteful and incorrect because an existing Flex template does not need to be discarded merely to add another input. The important design point is that Flex templates support custom resources and file inputs, so the existing template can be extended rather than rebuilt.