diff --git a/telethon/utils.py b/telethon/utils.py
index a5f95e9a..8d9cadc6 100644
--- a/telethon/utils.py
+++ b/telethon/utils.py
@@ -15,8 +15,10 @@ import os
 import pathlib
 import re
 import struct
+from tg_file_id.file_id import FileId, DocumentFileId, PhotoFileId
 from collections import namedtuple
 from mimetypes import guess_extension
+from typing import Union
 from types import GeneratorType
 
 from .extensions import markdown, html
@@ -1101,104 +1103,85 @@ def resolve_bot_file_id(file_id):
 
     For thumbnails, the photo ID and hash will always be zero.
     """
-    data = _rle_decode(_decode_telegram_base64(file_id))
-    if not data:
+    if not file_id:
         return None
-
-    # This isn't officially documented anywhere, but
-    # we assume the last byte is some kind of "version".
-    data, version = data[:-1], data[-1]
-    if version not in (2, 4):
+    # end if
+    if isinstance(file_id, str):
+        file = FileId.from_file_id(file_id)
+    elif not isinstance(file_id, FileId):
         return None
+    # end if
 
-    if (version == 2 and len(data) == 24) or (version == 4 and len(data) == 25):
-        if version == 2:
-            file_type, dc_id, media_id, access_hash = struct.unpack('<iiqq', data)
-        # elif version == 4:
-        else:
-            # TODO Figure out what the extra byte means
-            file_type, dc_id, media_id, access_hash, _ = struct.unpack('<iiqqb', data)
-
-        if not (1 <= dc_id <= 5):
-            # Valid `file_id`'s must have valid DC IDs. Since this method is
-            # called when sending a file and the user may have entered a path
-            # they believe is correct but the file doesn't exist, this method
-            # may detect a path as "valid" bot `file_id` even when it's not.
-            # By checking the `dc_id`, we greatly reduce the chances of this
-            # happening.
-            return None
-
+    if isinstance(file, DocumentFileId):
         attributes = []
-        if file_type == 3 or file_type == 9:
+        if file.type_id in (FileId.TYPE_VOICE, FileId.TYPE_AUDIO):
             attributes.append(types.DocumentAttributeAudio(
                 duration=0,
-                voice=file_type == 3
+                voice=file.type_id == FileId.TYPE_VOICE
             ))
-        elif file_type == 4 or file_type == 13:
+        elif file.type_id == FileId.TYPE_VIDEO or file.type_id == FileId.TYPE_VIDEO_NOTE:
             attributes.append(types.DocumentAttributeVideo(
                 duration=0,
                 w=0,
                 h=0,
-                round_message=file_type == 13
+                round_message=file.type_id == FileId.TYPE_VIDEO_NOTE
             ))
-        # elif file_type == 5:  # other, cannot know which
-        elif file_type == 8:
+        # elif file.type_id == FieldId.TYPE_DOCUMENT:  # other, cannot know which --> no attribute
+        elif file.type_id == FileId.TYPE_STICKER:
             attributes.append(types.DocumentAttributeSticker(
                 alt='',
                 stickerset=types.InputStickerSetEmpty()
             ))
-        elif file_type == 10:
+        elif file.type_id == FileId.TYPE_ANIMATION:
             attributes.append(types.DocumentAttributeAnimated())
+        # end if
 
         return types.Document(
-            id=media_id,
-            access_hash=access_hash,
+            id=file.id,
+            access_hash=file.access_hash,
             date=None,
             mime_type='',
             size=0,
             thumbs=None,
-            dc_id=dc_id,
+            dc_id=file.dc_id,
             attributes=attributes,
-            file_reference=b''
+            file_reference=file.file_reference if file.has_reference else b''
         )
-    elif (version == 2 and len(data) == 44) or (version == 4 and len(data) in (49, 77)):
-        if version == 2:
-            (file_type, dc_id, media_id, access_hash,
-                volume_id, secret, local_id) = struct.unpack('<iiqqqqi', data)
-        # else version == 4:
-        elif len(data) == 49:
-            # TODO Figure out what the extra five bytes mean
-            (file_type, dc_id, media_id, access_hash,
-                volume_id, secret, local_id, _) = struct.unpack('<iiqqqqi5s', data)
-        elif len(data) == 77:
-            # See #1613.
-            (file_type, dc_id, _, media_id, access_hash, volume_id, _, local_id, _) = struct.unpack('<ii28sqqq12sib', data)
-        else:
-            return None
+    elif not isinstance(file, PhotoFileId):  # e.g. WebLocationFileId
+        return None
+    # end if
 
-        if not (1 <= dc_id <= 5):
-            return None
+    # okey, so we're dealing with a photo.
+    assert isinstance(file, PhotoFileId)
+    photo_size = 's' if file.id or file.access_hash else 'x'
 
-        # Thumbnails (small) always have ID 0; otherwise size 'x'
-        photo_size = 's' if media_id or access_hash else 'x'
-        return types.Photo(
-            id=media_id,
-            access_hash=access_hash,
-            file_reference=b'',
-            date=None,
-            sizes=[types.PhotoSize(
+    foto_size = file.photosize
+    if isinstance(foto_size, (PhotoFileId.PhotosizeSourceLegacy, PhotoFileId.PhotosizeSourceThumbnail, PhotoFileId.PhotosizeSourceDialogPhotoSmall, PhotoFileId.PhotosizeSourceDialogPhotoBig, PhotoFileId.PhotosizeSourceStickersetThumbnail)):
+        sizes = [
+            types.PhotoSize(
                 type=photo_size,
                 location=types.FileLocationToBeDeprecated(
-                    volume_id=volume_id,
-                    local_id=local_id
+                    volume_id=foto_size.volume_id,
+                    local_id=foto_size.location_local_id,
                 ),
                 w=0,
                 h=0,
                 size=0
-            )],
-            dc_id=dc_id,
-            has_stickers=None
-        )
+            )
+        ]
+    else:
+        sizes = []
+    # end if
+
+    return types.Photo(
+        id=file.id,
+        access_hash=file.access_hash,
+        file_reference=file.file_reference,
+        date=None,
+        sizes=sizes,
+        dc_id=file.dc_id,
+        has_stickers=None
+    )
 
 
 def pack_bot_file_id(file):