Problem when importing PDF to CorelDraw

Hello Everyone!

I encounter a problem recently when importing PDF files into Corel Draw. These PDF files are exported from QGIS (maps) and it seems that every time I add them to Corel, there are some missing layers. This didn't happen to me before, so I am not sure if it's a problem of the settings in QGIS or something that I need to change in Corel. Thanks a lot in advanced!