crop/cut object to document size

I don't know what the descriptions look like in X6, but you can use Ctrl+A  for Mask->Select All (X5) or Mask->Select Entire Image (X7). That gives you a mask that is the same size as the document.

After creating that mask, you can use Image->Crop to Mask (X5) or Image->Crop Image to Mask (X7) to crop your object to that size.

Another way is to use CorelDraw
1. set the page size to requested size 3000x3000 + its bounding rectangle
2. import picture
3. position/move picture on page
4. trim picture by using rectangle
5. export result

points 4+5 can be automated by macro (and call macro by its shortcut or click on button)