Custom logo for sales invoices and quotations

1

How can I add my custom logo in sales invoice and sales quote?

2

See http://www.manager.io/guides/miscellaneous/adding-business-logo/

3

Also I would like to add stamp at the end of sales invoice and sales quote.

4

Then use Notes field at the bottom of sales invoice form.

5

I can only create text but I can’t upload an image in that field

6

The Notes field will accept HTML markup so you could inject inline image as HTML tag and it should work. You should consult someone who knows HTML to help you with this if you are not familiar with HTML.