program crash or file occupied after using CloseDocument()

[rodingbao]

1. When opening a new file using LoadFile if one PDF file was already opened and displayed, the number of thumbnails is correct, but the thumbnail of the first page is sometimes from the previous PDF file.
2. After using CloseDocument(); the PDF file still be occupied and cant be copy or deleted; sometime program crash directly

[rodingbao]

issue 2 closed, that was caused by another library.