无法将图像合并到垂直对齐并共享该文件。在这种情况下，最后一个图像文件将仅添加到mergeImage的末尾。请参阅以下代码：

import 'package:image/image.dart' as im;

final path = (await getTemporaryDirectory()).path;
var i = 0;
List<String> paths = [];

await for (final page in Printing.raster(pdf, dpi: 72)) {
  final png = await page.toPng();
  final file = File('$path/page-${i.toString().padLeft(3, '0')}.png');
  await file.writeAsBytes(png);
  print('Saved to ${file.absolute.path}');
  paths.add(file.absolute.path);

  i++;
  print('object');
}

int height = 0;
int width = im.decodeImage(File(paths.first).readAsBytesSync()).width;
for (var item in paths) {
  final image = im.decodeImage(File(item).readAsBytesSync());
  height += image.height + 10;
}

im.Image fullMergeImage;
int pos = 0;
for (var item in paths) {
  print('object');
  fullMergeImage = im.Image(width, height);
  final image = im.decodeImage(File(item).readAsBytesSync());
  im.copyInto(fullMergeImage, image, dstY: pos, blend: false);
  pos += image.height + 10;
}

final documentDirectory = await getTemporaryDirectory();
final file = new File(documentDirectory.path + '.png');
file.writeAsBytesSync(im.encodeJpg(fullMergeImage));

await Share.shareFiles([file.absolute.path], text: 'Great picture');