It can be difficult or impossible to select individual words in a PDF document in Evince when there are lines nearby that are offset by a non-whole multiple of the line spacing of the line that is being selected.  In the attached screenshot, the Chinese word in the far left column is almost impossible to select on its own, without getting other text boxes selected, especially if the mouse wanders up or down at all from the original starting y position as it is dragged horizontally over the word.

Probably the actual height of characters in the line, or the line spacing, should be checked when deciding if the vertical distance moved during text selection should cause other nearby lines to be selected or not.