I fixed UISearchDisplayController for iOS 7. So. Much. Pain.

FixUISearchDisplayController.m

static UIView *PSPDFViewWithSuffix(UIView *view, NSString *classNameSuffix) {
    if (!view || classNameSuffix.length == 0) return nil;

    UIView *theView = nil;
    for (__unsafe_unretained UIView *subview in view.subviews) {
        if ([NSStringFromClass(subview.class) hasSuffix:classNameSuffix]) {
            return subview;
        }else {
            if ((theView = PSPDFViewWithSuffix(subview, classNameSuffix))) break;
        }
    }
    return theView;
}

- (void)correctSearchDisplayFrames {
    // Update search bar frame.
    CGRect superviewFrame = self.searchDisplayController.searchBar.superview.frame;
    superviewFrame.origin.y = 0.f;
    self.searchDisplayController.searchBar.superview.frame = superviewFrame;

    // Strech dimming view.
    UIView *dimmingView = PSPDFViewWithSuffix(self.view, @"DimmingView");
    if (dimmingView) {
        CGRect dimmingFrame = dimmingView.superview.frame;
        dimmingFrame.origin.y = self.searchDisplayController.searchBar.frame.size.height;
        dimmingFrame.size.height = self.view.frame.size.height - dimmingFrame.origin.y;
        dimmingView.superview.frame = dimmingFrame;
    }
}

- (void)setAllViewsExceptSearchHidden:(BOOL)hidden animated:(BOOL)animated {
    [UIView animateWithDuration:animated ? 0.25f : 0.f animations:^{
        for (UIView *view in self.tableView.subviews) {
            if (view != self.searchDisplayController.searchResultsTableView &&
                view != self.searchDisplayController.searchBar) {
                view.alpha = hidden ? 0.f : 1.f;
            }
        }
    }];
}

// This fixes UISearchBarController on iOS 7. rdar://14800556
- (void)correctFramesForSearchDisplayControllerBeginSearch:(BOOL)beginSearch {
    if (PSPDFIsUIKitFlatMode()) {
        [self.navigationController setNavigationBarHidden:beginSearch animated:YES];
        dispatch_async(dispatch_get_main_queue(), ^{
            [self correctSearchDisplayFrames];
        });
        [self setAllViewsExceptSearchHidden:beginSearch animated:YES];
        [UIView animateWithDuration:0.25f animations:^{
            self.searchDisplayController.searchResultsTableView.alpha = beginSearch ? 1.f : 0.f;
        }];
    }
}

- (void)searchDisplayControllerWillBeginSearch:(UISearchDisplayController *)controller {
    [self correctFramesForSearchDisplayControllerBeginSearch:YES];
}

- (void)searchDisplayControllerDidBeginSearch:(UISearchDisplayController *)controller {
    [self correctSearchDisplayFrames];
}

- (void)searchDisplayControllerWillEndSearch:(UISearchDisplayController *)controller {
    [self correctFramesForSearchDisplayControllerBeginSearch:NO];
}

- (void)searchDisplayController:(UISearchDisplayController *)controller didShowSearchResultsTableView:(UITableView *)tableView {
    // HACK: iOS 7 requires a cruel workaround to show the search table view.
    if (PSPDFIsUIKitFlatMode()) {
        controller.searchResultsTableView.contentInset = UIEdgeInsetsMake(self.searchDisplayController.searchBar.frame.size.height, 0.f, 0.f, 0.f);
    }
}

Hello, it works !