invoice template change

Hi, I would like to help me how can I modify the invoice template that has the default, since the three that it brings by default I do not like are somewhat messy and not very clear.
What file is edited to generate an invoice as one wants it to come with the company logo and watermark if possible, buy the app print template but the template you create with it is not included in the general, only It is for printing and cannot be sent or the system generates them on a recurring basis and sends them to the emails of the clients

hi
when i enter the discount in the bills or invoices it is showing as percentage but i want it as an amount so how cai make it as an amount ?
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also regarding the tax is showing at he end of the invoice as a total but how can make each tax for each item in the invoice or bill