Use the convert argument '-define "pdf:use-cropbox=true"' when creating thumbnails. That way cropboxes, if present, gets respected for thumbnail generation.

src/documents/management/commands/document_importer.py

@@ -290,6 +290,7 @@ class Command(BaseCommand):
                             strip=True,
                             trim=False,
                             auto_orient=True,
+                            define="pdf:use-cropbox=true",
                             input_file=f"{thumbnail_path}[0]",
                             output_file=str(document.thumbnail_path),
                         )

src/documents/migrations/0012_auto_20160305_0040.py

@@ -94,6 +94,8 @@ def move_documents_and_create_thumbnails(apps, schema_editor):
                 "500x5000",
                 "-alpha",
                 "remove",
+                "-define",
+                "pdf:use-cropbox=true",
                 orig_target,
                 os.path.join(thumb_temp, "convert-%04d.png"),
             ),

src/documents/migrations/1021_webp_thumbnail_conversion.py

@@ -27,6 +27,7 @@ def _do_convert(work_package):
             strip=True,
             trim=False,
             auto_orient=True,
+            define="pdf:use-cropbox=true",
             input_file=f"{existing_thumbnail}[0]",
             output_file=str(converted_thumbnail),
         )

src/documents/migrations/1037_webp_encrypted_thumbnail_conversion.py

@@ -53,6 +53,7 @@ def _do_convert(work_package):
             strip=True,
             trim=False,
             auto_orient=True,
+            define="pdf:use-cropbox=true",
             input_file=f"{decrypted_thumbnail}[0]",
             output_file=str(converted_decrypted_thumbnail),
         )

src/documents/parsers.py

@@ -140,6 +140,7 @@ def run_convert(
     type=None,
     depth=None,
     auto_orient=False,
+    define=None,
     extra=None,
     logging_group=None,
 ) -> None:
@@ -158,6 +159,7 @@ def run_convert(
     args += ["-type", str(type)] if type else []
     args += ["-depth", str(depth)] if depth else []
     args += ["-auto-orient"] if auto_orient else []
+    args += ["-define", str(define)] if define else []
     args += [input_file, output_file]
 
     logger.debug("Execute: " + " ".join(args), extra={"group": logging_group})
@@ -229,6 +231,7 @@ def make_thumbnail_from_pdf(in_path, temp_dir, logging_group=None) -> str:
             strip=True,
             trim=False,
             auto_orient=True,
+            define="pdf:use-cropbox=true",
             input_file=f"{in_path}[0]",
             output_file=out_path,
             logging_group=logging_group,