Embed other files inside a PDF so they travel with it as one document. A report can carry the spreadsheet its figures came from, a drawing can carry its source file, and a reader can open the attachment from the paperclip panel. The attached files are stored whole inside the PDF, so the document grows by their full size.
Through the attachments or paperclip panel in their PDF reader. Most desktop readers support this; support in browser-based and mobile viewers is patchier, so do not rely on it for a critical delivery.
Any type - the file is embedded as opaque data. Bear in mind that some readers and mail gateways block opening executable attachments out of a PDF.
Sanitise PDF strips embedded files, along with JavaScript and other active content.
PDF/A restricts what may be embedded, so adding arbitrary attachments can break conformance. Attach first and convert to PDF/A afterwards, then validate the result.
Files are uploaded over an encrypted connection and processed on CoonTool's own server, not in your browser. The working copy is deleted automatically once the job is done, and in any case within 24 hours. Nothing is stored permanently and no account is required.