From Tracker Software PDF SDK
The method unlocks a portion of the page that was previously locked by a call to IIXC_Page::LockPageBlock.
HRESULT UnlockPageBlock([in] IXC_PageBlockData* pBlockData);
- [in] Pointer to IXC_PageBlockData structure that was previously passed to IIXC_Page::LockPageBlock.
Returns S_OK if operation was successful or error code in other cases.
IIXC_Page::LockPageBlock and IIXC_Page::UnlockPageBlock must be used as a pair. A call to the IIXC_Page::LockPageBlock function of the page establishes a temporary buffer that you can use to read or write pixel data. After you write to the temporary buffer, a call to IIXC_Page::UnlockPageBlock copies the pixel data in the buffer to the page.