diff --git a/setup.py b/setup.py
index b7fb4d8f1..0e9aa0449 100644
--- a/setup.py
+++ b/setup.py
@@ -140,12 +140,20 @@ def main():
     pl_spec = os.environ.get(PlatSpec_EnvVar, "")
     modspec = os.environ.get(ModulesSpec_EnvVar, "")
     
-    # TODO embed is_prepared in version file? - in principle, it could be arbitrary caller-given files
     with_prepare, pl_name, pdfium_ver, use_v8 = parse_pl_spec(pl_spec)
     modnames = parse_modspec(modspec, pl_name)
     
-    if ModuleRaw in modnames and with_prepare:
-        prepare_setup(pl_name, pdfium_ver, use_v8)
+    if ModuleRaw in modnames:
+        if with_prepare:
+            prepare_setup(pl_name, pdfium_ver, use_v8)
+        # TODO rewrite only if not with_prepare?
+        pdfium_info_file = ModuleDir_Raw/VersionFN
+        pdfium_info = read_json(pdfium_info_file)
+        if with_prepare:
+            pdfium_info["data_source"] = "internal"
+        else:
+            pdfium_info["data_source"] = "external"
+        write_json(pdfium_info_file, pdfium_info)
     run_setup(modnames, pl_name, pdfium_ver)
 
 
diff --git a/setupsrc/pypdfium2_setup/craft_packages.py b/setupsrc/pypdfium2_setup/craft_packages.py
index 980e50689..a33be42fd 100644
--- a/setupsrc/pypdfium2_setup/craft_packages.py
+++ b/setupsrc/pypdfium2_setup/craft_packages.py
@@ -129,7 +129,7 @@ def run_conda_build(recipe_dir, out_dir, args=[]):
 def _run_conda_bundle(args, pl_name, suffix, conda_args):
     
     os.environ["IN_"+PlatSpec_EnvVar] = pl_name + suffix
-    emplace_func = partial(prepare_setup, pl_name, args.pdfium_ver, args.use_v8)
+    emplace_func = partial(prepare_setup, pl_name, args.pdfium_ver, args.use_v8, is_conda=True)
     
     with CondaExtPlatfiles(emplace_func):
         run_conda_build(CondaDir/"bundle", CondaDir/"bundle"/"out", conda_args)
diff --git a/setupsrc/pypdfium2_setup/emplace.py b/setupsrc/pypdfium2_setup/emplace.py
index 5d3d60b3b..faf3977c4 100644
--- a/setupsrc/pypdfium2_setup/emplace.py
+++ b/setupsrc/pypdfium2_setup/emplace.py
@@ -44,7 +44,7 @@ def _get_pdfium_with_cache(pl_name, req_ver, req_flags, use_v8):
     build_pdfium_bindings(req_ver, flags=req_flags, compile_lds=compile_lds)
 
 
-def prepare_setup(pl_name, pdfium_ver, use_v8):
+def prepare_setup(pl_name, pdfium_ver, use_v8, is_conda=False):
     
     clean_platfiles()
     flags = ["V8", "XFA"] if use_v8 else []
@@ -53,8 +53,10 @@ def prepare_setup(pl_name, pdfium_ver, use_v8):
         # TODO add option for caller to pass in custom run_lds and headers_dir
         build_pdfium_bindings(pdfium_ver, flags=flags, guard_symbols=True, run_lds=[])
         shutil.copyfile(DataDir_Bindings/BindingsFN, ModuleDir_Raw/BindingsFN)
-        write_pdfium_info(ModuleDir_Raw, pdfium_ver, origin="system", flags=flags)
+        origin = "system" + ("_conda" if is_conda else "")
+        write_pdfium_info(ModuleDir_Raw, pdfium_ver, origin=origin, flags=flags)
         return [BindingsFN, VersionFN]
+    
     else:
         platfiles = []
         pl_dir = DataDir/pl_name
diff --git a/setupsrc/pypdfium2_setup/packaging_base.py b/setupsrc/pypdfium2_setup/packaging_base.py
index 4c5346a92..4c674af16 100644
--- a/setupsrc/pypdfium2_setup/packaging_base.py
+++ b/setupsrc/pypdfium2_setup/packaging_base.py
@@ -544,8 +544,8 @@ def parse_pl_spec(pl_spec, need_prepare=True):
     else:
         raise ValueError(f"Invalid binary spec '{pl_spec}'")
     
-    if pl_name == ExtPlats.system:
-        assert req_ver, "Version must be given explicitly for system target."
+    if pl_name == ExtPlats.system or need_prepare:
+        assert req_ver, "Version must be given explicitly for system or prepared targets."
         
     if req_ver:
         assert req_ver.isnumeric()
diff --git a/src/pypdfium2/version.py b/src/pypdfium2/version.py
index 11403a552..01f92e5b1 100644
--- a/src/pypdfium2/version.py
+++ b/src/pypdfium2/version.py
@@ -57,6 +57,7 @@ def _craft_desc(self, extra=[]):
         desc = ""
         if local_ver:
             desc += "+" + ".".join(local_ver)
+        
         return desc
     
     @cached_property
@@ -111,6 +112,8 @@ def desc(self):
             desc += ":{%s}" % ",".join(self.flags)
         if self.origin != "pdfium-binaries":
             desc += f"@{self.origin}"
+        if self.data_source != "internal":
+            desc += f"!{self.data_source}_source"  # external
         return desc
 
 # TODO(future) add bindings info (e.g. ctypesgen version, reference/generated, runtime libdirs)
@@ -218,6 +221,10 @@ def desc(self):
         - ``system``: Dynamically loaded from a standard system location using :func:`ctypes.util.find_library`.
     flags (tuple[str]):
         Tuple of pdfium feature flags. Empty for default build. (V8, XFA) for pdfium-binaries V8 build.
+    data_source (str):
+        Source of the bundled data files (binary/bindings/version). Possible values:\n
+        - ``internal`` if probably generated natively by setup code.
+        - ``external`` if provided by caller. Unsafe, can be arbitrary given files. This is evidence of a third-party build unless origin is system_conda (but not all third-party builds have to be external).
 """
 
 # -----