From http://aur.archlinux.org/packages.php?ID=52333

--- mupdf-0.9/apps/pdfapp.c
+++ mupdf-0.9/apps/pdfapp.c
@@ -817,11 +817,15 @@
 		break;
 
 	case 'j':
+		if (app->pany + app->image->h <= app->winh)
+			goto pagedown;
 		app->pany -= app->image->h / 10;
 		pdfapp_showpage(app, 0, 0, 1);
 		break;
 
 	case 'k':
+		if (app->pany >= 0)
+			goto pageup;
 		app->pany += app->image->h / 10;
 		pdfapp_showpage(app, 0, 0, 1);
 		break;
@@ -885,6 +889,7 @@
 	 */
 
 	case ',':
+		pageup:
 		panto = PAN_TO_BOTTOM;
 		if (app->numberlen > 0)
 			app->pageno -= atoi(app->number);
@@ -893,6 +898,7 @@
 		break;
 
 	case '.':
+		pagedown:
 		panto = PAN_TO_TOP;
 		if (app->numberlen > 0)
 			app->pageno += atoi(app->number);
@@ -902,7 +908,7 @@
 	case 'b':
 	case '\b': //backspace
-		panto = DONT_PAN;
+		panto = PAN_TO_TOP;
 		if (app->numberlen > 0)
 			app->pageno -= atoi(app->number);
 		else

@ -1067,7 +1073,12 @@
 				int isx = (modifiers & (1<<0));
 				int xstep = isx ? 20 * dir : 0;
 				int ystep = !isx ? 20 * dir : 0;
-				pdfapp_panview(app, app->panx + xstep, app->pany + ystep);
+ 				if (!isx && dir < 0 && app->pany + app->image->h <= app->winh)
+ 					pdfapp_onkey(app, 'j');
+ 				else if (!isx && dir > 0 && app->pany >= 0)
+ 					pdfapp_onkey(app, 'k');
+ 				else
+ 					pdfapp_panview(app, app->panx + xstep, app->pany + ystep);
 			}
 		}
 	}