static void Main(string[] args)
{
	PdfCommon.Initialize();

	var doc = PdfDocument.Load(@"d:\00\test_big.pdf");
	var page = doc.Pages[1];

	//target area
	var targetArea= new FS_RECTF() { left = 88, top = 586, right = 150, bottom = 546 };

	//Getting rows in target area
	//The bounded text would be placed into 'text'
	string text; 
	List<FS_RECTF> rects = GetBoundedTextInfo(page, targetArea, out text);

	//Test. Get the text bounded by found rectangles. Compare visually with text received earlier.
	//Looks like everything works fine.
	for (int i=0; i< rects.Count; i++)
	{
		string textForTest = page.Text.GetBoundedText(rects[i]);
	}
}

/// <summary>
/// Emulates GetTextInfo method for target area
/// </summary>
static List<FS_RECTF> GetBoundedTextInfo(PdfPage page, FS_RECTF rect, out string text)
{
	var cnt = page.Text.CountChars;
	List<FS_RECTF> ret = new List<FS_RECTF>();
	text = "";
	for (int i=0; i< cnt; i++)
	{
		var bbox = page.Text.GetCharBox(i);
		if (!IsIntersects(bbox, rect))
			continue; //The character does not intersects with target area.

		if (AnalizeCharBbox(ret, bbox))
			text += "\r\n"; //new row into ret collection  was added
		text += page.Text.GetCharacter(i);
	}
	return ret;
}

/// <summary>
/// Returns true if reactengles are intersected, False otherwise.
/// </summary>
static bool IsIntersects(FS_RECTF rect1, FS_RECTF rect2)
{
	if (rect1.right > rect2.left && rect1.right < rect2.right)
		if (rect1.bottom < rect2.top && rect1.bottom > rect2.bottom)
			return true; //rect 1 intersects with rect2
	return false; //the rectangles are not intersectedd
}

/// <summary>
/// Analyzes the current bounding box relatively the previous bbox.
/// If a new row was detected, adds new rectangle into ret collections and returns true.
/// Otherwise extend the last row for current bbox and returns false;
/// </summary>
private static bool AnalizeCharBbox(List<FS_RECTF> ret, FS_RECTF bbox)
{
	if (ret.Count == 0)
	{
		ret.Add(bbox);
		return false; //it's a first row
	}

	var prevBox = ret[ret.Count - 1];
	if (bbox.top < prevBox.bottom)
	{
		ret.Add(bbox);
		return true; //it's a new row;
	}
	else
	{
		prevBox.right = bbox.right;
		prevBox.top = Math.Max(prevBox.top, bbox.top);
		prevBox.bottom = Math.Min(prevBox.bottom, bbox.bottom);
		ret[ret.Count - 1] = prevBox;
		return false; //it is a not new row. Just extend a previouse row.
	}

}