Dynamic Action Bar (DAB) in File Previewers

01 / The Problem

Copilot was buried. Users consumed documents, but never used the AI beside them.

The previewer was the most-visited surface in M365 mobile — and the one with the lowest AI engagement. The intelligence was there; the bridge to it wasn't.

"The question wasn't 'how do we add AI to previewers?' — it was 'how do we make Copilot feel like it was always supposed to be here?'"

02 / The Insight

Evolve Copilot from "a button you tap" to "a dynamic action surface."

That became the Dynamic Action Bar (DAB) — a persistent, adaptive layer blending Copilot and native app actions into one always-present button at the bottom of every previewer. It had to flex across two very different content models:

Established

Files created outside AI — docs, sheets, decks, PDFs. Users come to read or edit; AI is a layer on top.

Word · Excel · PowerPoint · PDF

Model-forward

Content generated and refined by AI — images, Pages, emerging formats where AI is central.

Images · Pages · AI-generated outputs

03 / The Design

A system, not a screen.

Every decision was filtered through mobile constraints and one goal: consistency across surfaces.

01

Consistent placement

DAB anchors to the same spot across every previewer. Predictability is a feature.

02

Dual action states

Copilot and app actions share one surface — AI actions lead, native actions support.

03

Context stays intact

Copilot responses open in a half-sheet — users never lose sight of the document.

04

Designed for small screens

No cluttered toolbars, no disruptive mode switches. DAB stays visible without getting in the way.

End to End

DAB in previewer — end to end.

From opening a file to acting on AI output — DAB stays present, useful, and out of the way.

04 / Impact

Previewers became Copilot's highest-intent entry point.

~2%

Copilot engagement in WXP previewers before DAB

~15%

Copilot engagement in WXP previewers after DAB adoption

The Dynamic Action Bar is now the standard for how Copilot surfaces inside document-centric experiences across M365 mobile — a pattern designed once, deployed across hundreds of millions of installs.

05 / My Role

Sole designer, end to end.

Strategy & scope

Set direction and pressure-tested the spec with the PM.

Research & data

Grounded every decision in usage data, not assumptions.

Interaction model

Designed the DAB system and its action hierarchy.

System scaling

Extended one pattern across Word, Excel, PPT & PDF.

Leadership reviews

Presented at milestones; defended rationale to senior leaders.

Impact tracking

Read live engagement metrics weekly to validate and iterate.