Classic/Antique Car Repair: vw 1968 door, seam lines, latch assembly

Question
i have a 1968 beetle - the problem is when driving the door pops open???

Answer
With the phenomally tiny amount of info you gave it is hard to tell.

Are all the metal parts in the latch assembly there and in good shape?

Is the striker bar worn down?

Is the door aligned with the seam lines and is the gap the same on both doors?

When the door is shut, is it flush with the body panel and aligned top to bottom.

Does the door drop slightly when opened?

With this slight amount of info, it might be possible to help you.