Solve a Power Automate Base64 Coding issue

I have a problem with the conversion of base64 formatting of pdf file content in Power Automate .

I want to do the following steps:

Get the file content of a pdf file from OneDrive for business

Replace a string inside the pdf file content

Attach the new pdf file content to an email in the Outlook Send E-Mail connector.

I only need screenshots with the flow steps and especially the expressions to handle the data conversions.