Paragraph marks and hidden formatting symbols (¶) using Office JavaScript API code in Word add-in

Is it possible to add and remove paragraph marks and hidden formatting symbols(¶) using office js.

No, but you can to use the following code to insert breaks:

// Link to full sample: https://raw.githubusercontent.com/OfficeDev/office-js-snippets/prod/samples/word/50-document/manage-body.yaml
// Inserts a page break at the beginning of the document.
// Run a batch operation against the Word object model.
await Word.run(async (context) => {
  // Create a proxy object for the document body.
  const body = context.document.body;

  // Queue a command to insert a page break at the start of the document body.
  body.insertBreak(Word.BreakType.page, Word.InsertLocation.start);

  // Synchronize the document state by executing the queued commands, and return a promise to indicate task completion.
  await context.sync();

  console.log("Added a page break at the start of the document body.");
});

To submit a feature request for the Office JavaScript API, please post your idea to the Microsoft 365 Developer Platform Tech Community.