ysong,
To select data from a pdf, it's the "region" command that you need to use. It is best to select the region you want in the data pane, and drag it on the screen, it will automatically create it. If you don't see the data pane, you can make it show up by going to View->Data Pane. You can then convert it to PressTalk(Tools->Convert to PlanetPress Talk) and the region command will be correctly setup, you just have to assign it to your variable.
The parameters of the region command are left, top, right, botom, in that order. They are measure values and they form the region that you want to read the text from.
Hope that helps.
Regards,
Rapha