In Transform mode, press Shift to drag corner and constrain scale

`↑ Shift`

All hotkeys for Autodesk SketchBook (Windows)

Marking menu Marking menu 1	`1`
Marking menu Marking menu 2	`2`
Marking menu Marking menu 3	`3`
Marking menu Marking menu 4	`4`
Marking menu Marking menu 5	`5`
Marking menu Marking menu 6	`6`
Marking menu Interface controls	`1` then `Mouse right click`
Marking menu Tools	`2` then `Mouse right click`
Marking menu Brushes	`3` then `Mouse right click`
Marking menu Colors	`4` then `Mouse right click`
Marking menu Edit	`5` then `Mouse right click`
Marking menu File	`6` then `Mouse right click`
Tools Previous frame (animation mode)	`,`
Tools Previous frame (animation mode)	`<`
Tools Adjust size (brush mode)	`B`
Tools In Transform mode, press Shift to drag corner and constrain scale	`↑ Shift`
Hotkeys in SketchBook for Windows 10 OK	`⤶ Enter`
Tools Add layer (layers mode)	`Ctrl` + `L`
Hotkeys in SketchBook for Windows 10 New	`Ctrl` + `N`
Tools Invoke Perspective tool (perspective mode)	`P`
Tools Invoke Lasso selection (selection mode)	`L`
Tools Invoke Symmetry X (symmetry mode)	`X`
Tools Transform layer	`V`
Tools Hide UI (UI)	`T`
SketchBook for Mobile / T Toggle fullscreen UI	`⭾ Tab`
Tools Zoom / rotate / move canvas	`Spacekey`
Hotkeys in SketchBook for Windows 10 Open	`Ctrl` + `O`
Hotkeys in SketchBook for Windows 10 Save	`Ctrl` + `S`
Tools Save As	`Ctrl` + `↑ Shift` + `S`
Tools Print	`Ctrl` + `P`
SketchBook for Mobile Quit app	`Ctrl` + `Q`
Hotkeys in SketchBook for Windows 10 Undo	`Ctrl` + `Z`
Hotkeys in SketchBook for Windows 10 Redo	`Ctrl` + `Y`
Hotkeys in SketchBook for Windows 10 Cut	`Ctrl` + `X`
Hotkeys in SketchBook for Windows 10 Copy	`Ctrl` + `C`
Tools Copy Merged	`Ctrl` + `↑ Shift` + `C`
Hotkeys in SketchBook for Windows 10 Paste	`Ctrl` + `V`
Tools Select All	`Ctrl` + `A`
SketchBook for Mobile Clear selection	`Ctrl` + `D`
Tools Invert Selection	`Ctrl` + `↑ Shift` + `I`
Tools Adjust Opacity	`O`
Tools Adjust Slant	`/`
Tools Increase brush size	`]`
Tools Decrease brush size	`[`
Hotkeys in SketchBook for Windows 10 Color picker	`Alt`
Hotkeys in SketchBook for Windows 10 Color picker	`I`
SketchBook for Mobile Switch to last brush	`S`
Tools Add Group	`Ctrl` + `G`
Tools Merge with below	`Ctrl` + `E`
Tools Clear Layer	`⬅ Backspace`
SketchBook for Mobile Undo	`Del`
SketchBook for Mobile Fit canvas to window	`Ctrl` + `0`
Tools Actual size	`Ctrl` + `Alt` + `0`
Tools Rotate canvas left	`9`
Tools Rotate canvas right	`0`
Tools Previous image	`Page Up`
Tools Next image	`Page Down`
Tools Hide Lagoon	`Ctrl` + `J`
Tools Toggle Title bar on/off	`Ctrl` + `Alt` + `J`
SketchBook for Mobile Open Preference window	`Ctrl` + `,`
Tools SketchBook Help	`F1`
Tools Next frame	`.`
Tools Next frame	`>`
Tools Previous keyframe	`↑ Shift` + `,`
Tools Previous keyframe	`↑ Shift` + `<`
Tools Next keyframe	`↑ Shift` + `.`
Tools Next keyframe	`↑ Shift` + `>`
Tools Add keyframe (on next frame)	`Alt` + `.`
Tools Invoke Rectangle Selection	`M`
Tools Arrow key to move pixel	`← ↑ → ↓`
Hotkeys in SketchBook for Windows 10 Cancel	`Esc`
Tools Click the start point to confirm or Enter key to confirm	`Mouse left click`
Tools Invoke Crop tool	`C`
Tools Snap or not	`D`
Tools Invoke Symmetry Y	`Y`
Tools Ruler	`R`
Tools Ellipse	`E`
Tools French Curve	`F`
SketchBook for Mobile Undo	`Back`
SketchBook for Mobile Redo	`Forward`
SketchBook for Mobile Redo	`Ctrl` + `↑ Shift` + `Z`