Use Freehand Select 
to select crosses and backstitch within an area of any shape.
To select cross stitch designs with Freehand Select
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Click the Freehand Select
button on the toolbar, then drag to draw an irregular outline around the desired stitches.
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Choose Edit > Freehand Select, then drag to draw an irregular outline around the desired stitches.
When you release the mouse the area is closed automatically.