ENH: AppearanceStream: Generate new font resource for unicode

This enables generating a new unicode font resource in case of
text widget values that cannot be encoded with existing font
resources.

Author: PJBrs

pypdf/generic/_appearance_stream.py

@@ -1,11 +1,12 @@
 import re
 from dataclasses import dataclass
 from enum import IntEnum
+from io import BytesIO
 from typing import Any, Optional, Union, cast
 
 from .._codecs import fill_from_encoding
 from .._codecs.core_font_metrics import CORE_FONT_METRICS
-from .._font import Font
+from .._font import HAS_FONTTOOLS, Font
 from .._utils import logger_warning
 from ..constants import AnnotationDictionaryAttributes, BorderStyles, FieldDictionaryAttributes
 from ..generic import (
@@ -374,6 +375,17 @@ def __init__(
         except UnicodeEncodeError:
             encodable = False
 
+        if not encodable:
+            # If we have a font file, we can try to produce a new font resource with an encoding
+            # that does include the necessary characters.
+            if font.font_descriptor.font_file and HAS_FONTTOOLS and font.sub_type == "TrueType":
+                new_font = font.from_truetype_font_file(BytesIO(font.font_descriptor.font_file.get_data()))
+                if font:
+                    font = new_font
+                    font_resource = font.as_font_resource()
+                    font_name = f"/{font.name}"
+                    encodable = True
+
         if not encodable:
             logger_warning(
                 f"Text string '{text}' contains characters not supported by font encoding. "
@@ -384,9 +396,9 @@ def __init__(
 
         font_glyph_byte_map: dict[str, bytes]
         if isinstance(font.encoding, str):
-            font_glyph_byte_map = {
-                v: k.encode(font.encoding) for k, v in font.character_map.items()
-            }
+            font_glyph_byte_map = {}
+            for key, value in font.character_map.items():
+                font_glyph_byte_map[value] = key.encode(font.encoding)
         else:
             font_glyph_byte_map = {v: bytes((k,)) for k, v in font.encoding.items()}
             font_encoding_rev = {v: bytes((k,)) for k, v in font.encoding.items()}