protected void LoadDocument(IntPtr document)
{
_document = document;
NativePdfiumMethods.FPDF_GetDocPermissions(_document);
_formCallbacks = new NativePdfiumMethods.FPDF_FORMFILLINFO();
_formCallbacksHandle = GCHandle.Alloc(_formCallbacks);
_formCallbacks.version = 1;
_form = NativePdfiumMethods.FPDFDOC_InitFormFillEnvironment(_document, ref _formCallbacks);
NativePdfiumMethods.FPDF_SetFormFieldHighlightColor(_form, 0, 0xFFE4DD);
NativePdfiumMethods.FPDF_SetFormFieldHighlightAlpha(_form, 100);
NativePdfiumMethods.FORM_DoDocumentJSAction(_form);
NativePdfiumMethods.FORM_DoDocumentOpenAction(_form);
Bookmarks = new PdfBookmarkCollection();
LoadBookmarks(Bookmarks, NativePdfiumMethods.FPDF_BookmarkGetFirstChild(document, IntPtr.Zero));
}