diff --git a/CHANGELOG.md b/CHANGELOG.md
index 89eeac2..87960b3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,8 @@
 - Changed the temporary directory path to user's cache directory, which is more appropriate for storing cache files and avoids issues with unintended cleanup.
 - Fixed the isssue where extra metadata information was not being saved to M4B files when they have no chapters, ensuring that all metadata is correctly written to the output file.
 - Fixed sleep prevention process not ending if program exited using Ctrl+C or kill.
+- Improved automatic filename suffixing to better prevent overwriting files with the same name, even if they have different extensions.
+- Improvements in code and documentation.
 
 # 1.1.4
 - Fixed extra metadata information not being saved to M4B files, ensuring that all metadata is correctly written to the output file.
diff --git a/abogen/constants.py b/abogen/constants.py
index fd230c8..fa88ee7 100644
--- a/abogen/constants.py
+++ b/abogen/constants.py
@@ -31,6 +31,28 @@ LANGUAGE_DESCRIPTIONS = {
     "z": "Mandarin Chinese",
 }
 
+# Supported sound formats
+SUPPORTED_SOUND_FORMATS = [
+    "wav",
+    "mp3",
+    "opus",
+    "m4b",
+    "flac",
+]
+
+# Supported subtitle formats
+SUPPORTED_SUBTITLE_FORMATS = [
+    "srt",
+    "ass",
+]
+
+# Supported input formats
+SUPPORTED_INPUT_FORMATS = [
+    "epub",
+    "pdf",
+    "txt",
+]
+
 # Supported languages for subtitle generation
 # Currently, only 'a (American English)' and 'b (British English)' are supported for subtitle generation.
 # This is because tokens that contain timestamps are not generated for other languages in the Kokoro pipeline.
diff --git a/abogen/conversion.py b/abogen/conversion.py
index bcba600..94fc9a8 100644
--- a/abogen/conversion.py
+++ b/abogen/conversion.py
@@ -10,12 +10,13 @@ from PyQt5.QtWidgets import QCheckBox, QVBoxLayout, QDialog, QLabel, QDialogButt
 import soundfile as sf
 from abogen.utils import clean_text, create_process, get_user_cache_path
 from abogen.constants import (
-    PROGRAM_NAME,
     LANGUAGE_DESCRIPTIONS,
     SAMPLE_VOICE_TEXTS,
     COLORS,
     CHAPTER_OPTIONS_COUNTDOWN,
     SUBTITLE_FORMATS,
+    SUPPORTED_SOUND_FORMATS,
+    SUPPORTED_SUBTITLE_FORMATS,
 )
 from abogen.voice_formulas import get_new_voice
 import abogen.hf_tracker as hf_tracker
@@ -425,29 +426,19 @@ class ConversionThread(QThread):
                 )
             # Find a unique suffix for both folder and merged file, always
             counter = 1
+            allowed_exts = set(SUPPORTED_SOUND_FORMATS + SUPPORTED_SUBTITLE_FORMATS)
             while True:
                 suffix = f"_{counter}" if counter > 1 else ""
                 chapters_out_dir_candidate = os.path.join(
                     parent_dir, f"{base_name}{suffix}_chapters"
                 )
-                merged_file_candidate = os.path.join(
-                    parent_dir, f"{base_name}{suffix}.{self.output_format}"
+                # Only check for files with allowed extensions (extension without dot, case-insensitive)
+                clash = any(
+                    os.path.splitext(fname)[0] == f"{base_name}{suffix}" and
+                    os.path.splitext(fname)[1][1:].lower() in allowed_exts
+                    for fname in os.listdir(parent_dir)
                 )
-                merged_srt_candidate = (
-                    os.path.splitext(merged_file_candidate)[0] + ".srt"
-                )
-                if (
-                    not os.path.exists(chapters_out_dir_candidate)
-                    and (
-                        not merge_chapters_at_end
-                        or not os.path.exists(merged_file_candidate)
-                    )
-                    and (
-                        self.subtitle_mode == "Disabled"
-                        or not merge_chapters_at_end
-                        or not os.path.exists(merged_srt_candidate)
-                    )
-                ):
+                if not os.path.exists(chapters_out_dir_candidate) and not clash:
                     break
                 counter += 1
             if save_chapters_separately and total_chapters > 1: