Tabs and windows

SumatraPDF can open documents in tabs inside one window, or in separate windows. Which you get depends on two independent settings plus optional command-line flags.

The two settings #

Setting	Default	What it does
`UseTabs`	`true`	New documents open as tabs in an existing window instead of always spawning a new window
`ReuseInstance`	`true`	Opening a file from Explorer or the command line reuses an already running SumatraPDF process

Both live in advanced settings (Settings → Advanced Options...).

Common confusion: tabs enabled but new window every time #

If UseTabs = true but ReuseInstance = false, each file is opened by a new process, so you always get a separate window — tabs only apply within one process.

Fix: set ReuseInstance = true and restart SumatraPDF.

This is the most frequent tabs question on the forum.

When settings take effect #

Setting	Restart required?
`ReuseInstance`	No — takes effect on the next file open
`UseTabs`	Yes — close and restart SumatraPDF

You can also toggle at runtime (ver 3.7+):

Ctrl + K → Toggle Reuse Instance (CmdToggleReuseInstance)
Ctrl + K → Toggle Use Tabs (CmdToggleUseTabs) — affects new windows only; switching between tabbed and non-tabbed layout for an existing window may still need a restart

Command-line flags #

Flag	Effect
`-new-window`	Open the file in a new window even when `UseTabs = true` (ver 3.2+)
`-reuse-instance`	Send the file to an already running instance (mainly for DDE and scripts). For normal use, prefer the `ReuseInstance` setting

-reuse-instance is not needed for everyday double-click opening when ReuseInstance = true.

Multiple instances #

If several SumatraPDF processes are already running (for example because ReuseInstance = false), behavior of -reuse-instance is undefined — the file may go to any instance.

To force a single instance, keep ReuseInstance = true and close extra windows.

Session restore #

With RestoreSession = true, SumatraPDF reopens tabs (and window positions) from the last session on startup. See How we store settings.

-for-testing deliberately skips session restore and does not save settings.

Keyboard shortcuts for tabs #

See Keyboard shortcuts:

Ctrl + Tab / Ctrl + Shift + Tab — next / previous tab
Ctrl + W or q — close current tab
Ctrl + Shift + N — open current document in a new window
Alt + 1 … Alt + 8, Alt + 9 (last tab) — jump to tab by number

Use the command palette: type @ to switch tabs by name.

Home tab #

When UseTabs = true, an empty window may show a Home tab. Set NoHomeTab = true in advanced settings to skip it. You can close the Home tab when other tabs are open; reopen it with Ctrl + K → Show Start Page if needed.