diff --git a/partitioncloud/modules/albums.py b/partitioncloud/modules/albums.py
index 7cb71a4..7f1334e 100644
--- a/partitioncloud/modules/albums.py
+++ b/partitioncloud/modules/albums.py
@@ -3,7 +3,9 @@
 Albums module
 """
 import os
+import pypdf
 import shutil
+
 from uuid import uuid4
 from typing import TypeVar
 
@@ -263,6 +265,12 @@ def add_partition(album_uuid):
     else:
         partition_type = "file"
 
+        try:
+            pypdf.PdfReader(request.files["file"])
+            request.files["file"].seek(0)
+        except (pypdf.errors.PdfReadError, pypdf.errors.PdfStreamError):
+            error = _("Invalid PDF file")
+
     if error is not None:
         flash(error)
         return redirect(request.referrer)
diff --git a/partitioncloud/modules/thumbnails.py b/partitioncloud/modules/thumbnails.py
index 36dc7c1..2513af7 100644
--- a/partitioncloud/modules/thumbnails.py
+++ b/partitioncloud/modules/thumbnails.py
@@ -2,6 +2,7 @@
 Thumbnails
 """
 import os
+import pypdf
 
 from flask import current_app, abort, Blueprint, send_file
 
@@ -14,13 +15,18 @@ def generate_thumbnail(source, dest):
     """
     Generates a thumbnail with 'convert' (ImageMagick)
     """
-    os.system(
-        f'/usr/bin/convert -thumbnail\
-        "178^>" -background white -alpha \
-        remove -crop 178x178+0+0 \
-        {source}[0] \
-        {dest}'
+    try:
+        pypdf.PdfReader(source) # Check if file is really a PDF
+    except (pypdf.errors.PdfReadError, pypdf.errors.PdfStreamError):
+        return
+
+    command = (
+        f"gs -dQUIET -dSAFER -dBATCH -dNOPAUSE -dNOPROMPT -dMaxBitmap=500000000 \
+        -dAlignToPixels=0 -dGridFitTT=2 -sDEVICE=png16m -dBackgroundColor=16#FFFFFF -dTextAlphaBits=4 \
+        -dGraphicsAlphaBits=4 -r72x72 -dPrinted=false -dFirstPage=1 -dPDFFitPage -g356x356 \
+        -dLastPage=1 -sOutputFile={dest} {source}"
     )
+    os.system(command)
 
 def serve_thumbnail(partition_file, thumbnail_file):
     """
@@ -32,6 +38,9 @@ def serve_thumbnail(partition_file, thumbnail_file):
     if not os.path.exists(thumbnail_file):
         generate_thumbnail(partition_file, thumbnail_file)
 
+        if not os.path.exists(thumbnail_file):
+            abort(404)
+
     return send_file(thumbnail_file)