You can interrupt APM while running. No data will be lost or corrupted. The started sub-operations will complete. The pages will be made-up to the point where you interrupted APM.
To interrupt APM while running
Press the Escape key.
If APM does not detect it immediately, press the Escape key again.
See the note for more details
Note
The APM process contains of several loops: loop of pages, loop of shapes, loop of articles, loop of fitting methods. For the performance reasons, non all loops detect the Escape key press. Therefore, it may happen that, when you pressed the Escape key, the software was running in the loop that does not detect the key press. In such a case, press the Escape key again and again (do not hold it pressed, but just press in quick sequence) until the software detects it.