From Tracker Software PDF SDK
The Invert method inverts the colors of the entire page or a specified rectangular area within the page. The result is similar to a photographic negative.
HRESULT Invert([in] RECT* stRect);
- [in] Pointer to a RECT structure which defines the rectangular area where colors should be inverted. If this parameter is NULL, the entire page will be inverted.
Note:Please note that processing part of the page is not supported for some internal formats. For example, it is not supported for indexed images, because the pixels in such images do not contain the color, but the index into a color table (or palette) which is common for the entire page.
Returns S_OK if operation was successful or error code in other cases.