How do I learn about keyboard shortcuts?

Document Editor

Here are some shortcuts for using the document editor:

ActionKeyResult
Rotate objectOptionSwitch snap to 45 degree positions on or off
Rotate objectCommandRotate all selected objects or just the one under the mouse. This key toggles the default set under Posterino > Preferences... > General > Apply mouse operation to all selected objects.
Rotate objectShiftRotate on 45 degree steps only
Size objectOptionSwitch snap to guides on or off. Toggles the state chosen under Layout > Snap to Guides.
Selected objectOption-Down ArrowMove the object one step backward (regarding the hierarchy of objects)
Selected objectOption-Up ArrowMove the object one step forward (regarding the hierarchy of objects)
 Cursor KeysMove the selection to the next graphic object
 Command-Arrow KeysMove the selected graphic object one pixel
 Command-Shift- Arrow KeysMove the selected graphic object ten pixel
 Pinch to ZoomZoom document

Image Crop Mode

Here are some shortcuts when using the image crop mode:

ActionKey / GestureResult
Crop ModeReturnGo into image crop mode using the selected image object.
Crop ModeReturnEnd the image crop mode making changes permanent.
Crop ModeESC / BackspaceEnd the image crop mode without changing the crop
Move ImageLeft Arrow / Up Arrow / Right Arrow / Down ArrowMove the image in small steps
Move ImageShift-Left Arrow / Shift-Up Arrow / Shift-Right Arrow / Shift-Down ArrowMove the image in large steps
Rotate ImageCommand-Left Arrow / Command-Right ArrowRotate the image size in small steps
Rotate ImageCommand-Shift-Left Arrow / Command-Shift-Right ArrowRotate the image size in large steps
Rotate ImageRotation Gesture (two finger rotation)Rotate the image
Size ImageCommand-Up Arrow / Command-Down ArrowSize the image size in small steps
Size ImageCommand-Shift-Up Arrow / Command-Shift-Down ArrowSize the image size in large steps
Size ImagePinch to ZoomChange the image size
Size ImageShift-Pinch to ZoomChange the image size in large steps
 RReset image crop

Text Edit Mode

Here are some shortcuts when editing text object:

ActionKey / GestureResult
Text Edit ModeReturnGo into text edit mode using the selected text object.
Text Edit ModeCommand-ReturnEnd the text edit session making changes permanent.
Text Edit ModeESCEnd the text edit session without making changes permanent.