Brochures, a product spec sheet or sales sheet are a great way to present the user with a clear product or service. Summarize your offering in a single, concise document and ask your user for their thoughts. Not only is the practice of buidling the documnet a worthwhile feat for your team but it also provides a stimulus for users to react to. Does the product respond to their pain points? Is it complete? What aspects are most or least likely to provdie value? Finally, you can ask what the user would be willing to pay for the product.
Build your brochure, product spec or sales sheet when you have a clear idea of the solution you intend to offer. Clearly the solution will evolve as you get more feedback from users but you need to have a product to summarize in the document in order for it to be useful as a Solution Validation tool.
Brochures and sales sheets give potential users a stimulus to assess and react to. They give users clearly outlined features, services and solution proposals to connect with and respond to with feedback.
You can always create and print your own brochure in Word, or make a scrappy prototype by hand if you're more focused on content than presentation, but there are online tools that can help too. Check out Canva, Adobe Spark, Vistaprint or Befunky for builders and inspiration.