Product Manager usually is the business side of building a product. Which means a product manager needs to think about what market to serve, which problems to solve and how to solve that profitably. He does that by building a product which addresses the market problems with the right feature sets and marketing it to get a profitable outcome. In that process he is responsible for collaborating and directing a set of cross functional teams which could include marketing, sales, engineering, finance and project management.
Generally speaking Project Managers manage projects which have definite start date and an end date. They are typically responsible for managing resources, allocations, methodologies and schedules. Their ability to stay on scope, schedule, plan and budget enables a successful delivery of the project. Their teams would typically include engineering and business analysis resources.
Another wide observation is that you will see Product Managers on the product (software, hardware, engineering etc) side of the world, while Project Managers are quite often seen in services oriented businesses (IT Services, Consulting, Construction etc)
A simplification of these roles would be –
Product managers own “What” and “Why”.
Project managers own “How” and “When”.
A good product manager is someone who can see ‘patterns’ very well. It means that in a given market place, you can see a ‘unsolved problem’ or ‘unfulfilled need’ and you have the passion to build a solution that will address the marketplace as a whole and not just the individual constituents. Add to that some good writing, prototyping, user experience, marketing and team skills – you will have the necessary recipe to do product management.
In enterprise software companies, many Product Managers come in typically with functional or domain expertise. So having that would help if you are looking in the enterprise software market.
Also many come with Consulting background. This typically exposes them to problems businesses face or unfulfilled needs in a consumer marketplace. That experience to understand it and propose building a solution is another way to get into product management.
One can also move into product management via ‘doing things’. Go build a product, an app or a site. Use that experience and sell why a potential employer should consider you for a job in product management.
As for me – I came into product management by accident rather than design, I came in with the consulting and technology experience mixed with functional expertise, so while at consulting I was solving similar problems for a wide variety of industries and that led to a product company looking to design products and serve a market with similar solutions.