PDF doc with eSign and protected is after sending over email again not protected

i think i solved the first point,

Just after answering I saw your message that you had solved your first issue. I merely was too lazy then to edit my answer. 😉

in your answer you mean that Apple`s preview app can rewrite (change) the PDF? I thought that PDF is secured against changes...

A PDF signature does not prevent changes to be applied to a document. It merely allows to detect them.

A PDF signature contains the information which byte ranges of the PDF file are signed and (implicitly or explicitly) a hash value of the bytes in those byte ranges. (Commonly only byte ranges are accepted covering the whole PDF revision created by the signer except the signature value itself.) These information are cryptographically secured using the private key of the signer which can be checked using the associated public key.

Nothing in this structure prevents a program to change the PDF.

But a recipient expecting the signed PDF can test

• whether the expected signature is there; otherwise, someone has removed it;
• whether the signature is from the expected signer by inspecting the cryptographic properties of the signature; otherwise someone manipulated the document and replaced the signature;
• whether the hash value in the signature matches the actual hash value of the signed byte ranges; otherwise someone has manipulated the signed byte ranges;
• whether the signed byte ranges cover the whole signed revision except the signature value; otherwise someone might have manipulated unsigned parts;
• whether there are no additions added after the signed revision with newer revisions; otherwise someone has added content.

(Depending on the kind of signatures applied, specific added content in newer revisions may be considered allowed; this is used for e.g. for forms to allow fill-ins and additional signatures after the first signature.)

Adobe Acrobat executes these checks on signed PDFs. Many previewers don't. On the other hand there are web services for checking PDF signatures, e.g. the European Commission DSS Demonstration WebApp .