pdfAttachFileEx

Fully documented elsewhere — cross-referenced here only to satisfy this volume's own completeness (see Bookmarks, Articles, Page Labels, and Structure-Tree Binding's scope note: these three happen to share the pdfA-prefix naming accident with this volume's real content, but their authoritative homes are in V17):

• pdfAppend — append a new blank page to the document (locks the document mutex around the append for thread safety). See V17 Import & Output, E01_DocumentLifecycle.
• pdfAttachFile / pdfAttachFileEx — attach a file (from a path, or from an in-memory buffer respectively) to the document's embedded-file name tree, with an optional description and compression flag. See V17 Import & Output, E03_EmbeddedFiles.

C# (P/Invoke)

public static extern int pdfAttachFileExA(IntPtr IPDF, IntPtr Buffer, uint BufSize, [MarshalAs(UnmanagedType.LPStr)] string FileName, [MarshalAs(UnmanagedType.LPStr)] string Description, [MarshalAs(UnmanagedType.Bool)] bool Compress);
public static extern int pdfAttachFileExW(IntPtr IPDF, IntPtr Buffer, uint BufSize, [MarshalAs(UnmanagedType.LPWStr)] string FileName, [MarshalAs(UnmanagedType.LPWStr)] string Description, [MarshalAs(UnmanagedType.Bool)] bool Compress);