Do I need PLM if I already have good PDM?

Only if the pain you're trying to solve lives outside engineering — cross-department change approval, as-built vs. as-designed reconciliation, quality traceability, or supplier/sourcing integration. If your CAD revision control is solid and your problems are still confined to engineering, PDM alone is often the right-sized tool, and adding a full PLM platform on top can be more process overhead than the team needs yet.

Is Git (or another software version control system) a form of PDM?

It plays a similar role for code — version history, branching, merge/check-in workflow — but general-purpose version control systems aren't built for CAD-specific needs like managing complex assembly reference structures, automatic BOM roll-up, or CAD-file-aware check-out locking that prevents two engineers from corrupting the same binary assembly file simultaneously. That said, some engineering teams do use Git (or Git-based PDM add-ons) for CAD, and the underlying "control who can change what, and track every version" concept is genuinely the same idea applied to a different kind of file.

What is an ECR/ECO/ECN, specifically?

An Engineering Change Request (ECR) proposes a change and routes it for review. Once approved, it becomes an Engineering Change Order (ECO), which authorizes the actual change to be implemented. An Engineering Change Notice (ECN) is the formal notification, once the change is released, telling every affected department (manufacturing, quality, sourcing, service) that the new revision is now the official one to use.

Does PLM cover only physical, mechanical parts?

No — modern PLM platforms increasingly manage electrical BOMs, PCB/EDA design data, embedded software/firmware versions, and documentation alongside mechanical CAD, because a complex product's full bill of materials is rarely mechanical-only. This is one of the practical reasons companies outgrow standalone PDM: mechanical-only CAD vaulting doesn't capture the electrical or software side of a mechatronic product.

Can a company run PLM without ever adopting formal PDM software?

In principle a very small operation could manage CAD files manually and still call some broader system "PLM," but in practice this is fragile and uncommon at any real scale — the moment more than a couple of engineers touch the same assembly, informal file management breaks down (overwritten files, lost revision history, no single source of truth), which is exactly the problem PDM was built to solve. Nearly every mature PLM deployment includes a real PDM capability underneath it.

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PDM vs. PLM

They aren't two competing products for the same job. PDM is the CAD-data vault engineering lives inside; PLM is the cross-enterprise system that usually contains it.

Ask a design engineer what manages their CAD files and revisions, and the honest answer is PDM — check-in/check-out, revision history, an as-designed bill of materials pulled straight from the assembly tree. Ask a program manager what tells them the true, current state of a product across engineering, manufacturing, sourcing, quality, and service, years after it shipped, and the honest answer is PLM. Both statements can be true about the same company at the same time, because PDM (Product Data Management) is not a smaller competitor to PLM (Product Lifecycle Management) — it is the engineering-data foundation that most real-world PLM deployments are built directly on top of.