Text formatting details like table lines or borders are removed when selected text is encrypted with Clipboard's Encrypt or ‘Encrypt & Sign’ feature.
Storing the table formattings or alignment details is the function of an advance editor like Word, Excel or 'Outlook Email' editor, and if that Word file or Outlook email is encrypted, we will not lose the table lines / borders. The very reason we prefer advance editors like word or excel rather than notepad.
Same has notepad editor, Clipboard feature is introduced just to address plain text and not for information like table borders etc.
As we see this is by design and Clipboard is made just to address the text encryption needs, we advise users to store formatted text in an advance editor and encrypt that file with Encryption Software, in order to retain the formatting or table lines/border properties.