diff --git a/cpdf.ml b/cpdf.ml
index 516d2f9..32ee20f 100644
--- a/cpdf.ml
+++ b/cpdf.ml
@@ -1965,38 +1965,6 @@ let remove_unused_resources_page pdf n page =
 let remove_unused_resources pdf =
   Cpdfpage.process_pages (ppstub (remove_unused_resources_page pdf)) pdf (ilist 1 (Pdfpage.endpage pdf))
 
-(* Indent bookmarks in each file by one and add a title bookmark pointing to the first page. *)
-let add_bookmark_title filename use_title pdf =
-  let title =
-    if use_title then
-      match Cpdfmetadata.get_info_utf8 pdf "/Title", Cpdfmetadata.get_xmp_info pdf "/Title" with
-        "", x | x, "" | _, x -> x
-    else
-      Filename.basename filename
-  in
-  let marks = Pdfmarks.read_bookmarks pdf in
-  let page1objnum =
-    match Pdfpage.page_object_number pdf 1 with
-      None -> error "add_bookmark_title: page not found"
-    | Some x -> x
-  in
-  let newmarks =
-      {Pdfmarks.level = 0;
-       Pdfmarks.text = title;
-       Pdfmarks.target = Pdfdest.XYZ (Pdfdest.PageObject page1objnum, None, None, None);
-       Pdfmarks.isopen = false}
-    ::map (function m -> {m with Pdfmarks.level = m.Pdfmarks.level + 1}) marks
-  in
-    Pdfmarks.add_bookmarks newmarks pdf
-
-let bookmarks_open_to_level n pdf =
-  let marks = Pdfmarks.read_bookmarks pdf in
-  let newmarks =
-    map
-      (fun m -> {m with Pdfmarks.isopen = m.Pdfmarks.level < n})
-      marks
-  in
-    Pdfmarks.add_bookmarks newmarks pdf
 
 let create_pdf pages pagesize =
   let page =
@@ -2006,5 +1974,3 @@ let create_pdf pages pagesize =
   in
     let pdf, pageroot = Pdfpage.add_pagetree (many page pages) (Pdf.empty ()) in
       Pdfpage.add_root pageroot [] pdf
-
-
diff --git a/cpdf.mli b/cpdf.mli
index 6c0d03e..42241ff 100644
--- a/cpdf.mli
+++ b/cpdf.mli
@@ -138,10 +138,9 @@ val image_resolution : Pdf.t -> int list -> float -> (int * string * int * int *
 
 val copy_box : string -> string -> bool -> Pdf.t -> int list -> Pdf.t
 
-val add_bookmark_title : string -> bool -> Pdf.t -> Pdf.t
 
 val remove_unused_resources : Pdf.t -> Pdf.t
 
-val bookmarks_open_to_level : int -> Pdf.t -> Pdf.t
+
 
 val create_pdf : int -> Pdfpaper.t -> Pdf.t
diff --git a/cpdfbookmarks.ml b/cpdfbookmarks.ml
index dc7fd92..8be3464 100644
--- a/cpdfbookmarks.ml
+++ b/cpdfbookmarks.ml
@@ -359,3 +359,37 @@ let name_of_spec encoding marks (pdf : Pdf.t) splitlevel spec n filename startpa
             else
               process_others encoding marks pdf splitlevel filename n startpage endpage
               (implode before ^ fill (length percents) n ^ implode after)
+
+(* Indent bookmarks in each file by one and add a title bookmark pointing to the first page. *)
+let add_bookmark_title filename use_title pdf =
+  let title =
+    if use_title then
+      match Cpdfmetadata.get_info_utf8 pdf "/Title", Cpdfmetadata.get_xmp_info pdf "/Title" with
+        "", x | x, "" | _, x -> x
+    else
+      Filename.basename filename
+  in
+  let marks = Pdfmarks.read_bookmarks pdf in
+  let page1objnum =
+    match Pdfpage.page_object_number pdf 1 with
+      None -> error "add_bookmark_title: page not found"
+    | Some x -> x
+  in
+  let newmarks =
+      {Pdfmarks.level = 0;
+       Pdfmarks.text = title;
+       Pdfmarks.target = Pdfdest.XYZ (Pdfdest.PageObject page1objnum, None, None, None);
+       Pdfmarks.isopen = false}
+    ::map (function m -> {m with Pdfmarks.level = m.Pdfmarks.level + 1}) marks
+  in
+    Pdfmarks.add_bookmarks newmarks pdf
+
+let bookmarks_open_to_level n pdf =
+  let marks = Pdfmarks.read_bookmarks pdf in
+  let newmarks =
+    map
+      (fun m -> {m with Pdfmarks.isopen = m.Pdfmarks.level < n})
+      marks
+  in
+    Pdfmarks.add_bookmarks newmarks pdf
+
diff --git a/cpdfbookmarks.mli b/cpdfbookmarks.mli
index f4a8a35..ade5d69 100644
--- a/cpdfbookmarks.mli
+++ b/cpdfbookmarks.mli
@@ -16,3 +16,6 @@ val list_bookmarks : json:bool -> Cpdfmetadata.encoding -> int list -> Pdf.t ->
 val name_of_spec : Cpdfmetadata.encoding ->
            Pdfmarks.t list ->
            Pdf.t -> int -> string -> int -> string -> int -> int -> string
+
+val add_bookmark_title : string -> bool -> Pdf.t -> Pdf.t
+val bookmarks_open_to_level : int -> Pdf.t -> Pdf.t
diff --git a/cpdfcommand.ml b/cpdfcommand.ml
index e7d11ab..40639b4 100644
--- a/cpdfcommand.ml
+++ b/cpdfcommand.ml
@@ -3038,7 +3038,7 @@ let go () =
                       let pdfs =
                         if args.merge_add_bookmarks then
                           map2
-                            (fun filename pdf -> Cpdf.add_bookmark_title filename args.merge_add_bookmarks_use_titles pdf)
+                            (fun filename pdf -> Cpdfbookmarks.add_bookmark_title filename args.merge_add_bookmarks_use_titles pdf)
                             (map (function InFile s -> s | StdIn -> "" | AlreadyInMemory _ -> "") names)
                             pdfs
                         else
@@ -3852,7 +3852,7 @@ let go () =
         Cpdffont.embed_missing_fonts args.path_to_ghostscript args.gs_quiet fi fo
   | Some (BookmarksOpenToLevel n) ->
       let pdf = get_single_pdf args.op false in
-        write_pdf false (Cpdf.bookmarks_open_to_level n pdf)
+        write_pdf false (Cpdfbookmarks.bookmarks_open_to_level n pdf)
   | Some CreatePDF ->
       let pdf = Cpdf.create_pdf args.createpdf_pages args.createpdf_pagesize in
         write_pdf false pdf