com.aspose.words

Example:

Document doc = new Document(getMyDir() + "Textboxes in drawing canvas.docx");

// This gets a live collection of all shape nodes in the document
NodeCollection shapeCollection = doc.getChildNodes(NodeType.SHAPE, true);

// Since we will be adding/removing nodes, it is better to copy all collection
// into a fixed size array, otherwise iterator will be invalidated
Node[] shapes = shapeCollection.toArray();

for (Node node : shapes) {
    Shape shape = (Shape) node;
    // Filter out all shapes that we don't need
    if (shape.getShapeType() == ShapeType.TEXT_BOX) {
        // Create a new shape that will replace the existing shape
        Shape image = new Shape(doc, ShapeType.IMAGE);

        // Load the image into the new shape
        image.getImageData().setImage(getImageDir() + "Windows MetaFile.wmf");

        // Make new shape's position to match the old shape
        image.setLeft(shape.getLeft());
        image.setTop(shape.getTop());
        image.setWidth(shape.getWidth());
        image.setHeight(shape.getHeight());
        image.setRelativeHorizontalPosition(shape.getRelativeHorizontalPosition());
        image.setRelativeVerticalPosition(shape.getRelativeVerticalPosition());
        image.setHorizontalAlignment(shape.getHorizontalAlignment());
        image.setVerticalAlignment(shape.getVerticalAlignment());
        image.setWrapType(shape.getWrapType());
        image.setWrapSide(shape.getWrapSide());

        // Insert new shape after the old shape and remove the old shape
        shape.getParentNode().insertAfter(image, shape);
        shape.remove();
    }
}

doc.save(getArtifactsDir() + "Shape.ReplaceTextboxesWithImages.docx");