How to convert string to pfd in Apex, I am sending pdf from SFDC to other application through REST Api, Pdf is not getting open in destination application.
You can use Visualforce for this, setting apex:page
renderAs="pdf" or instead using PageReference
getContentAsPDF. Either of these ensures that the data is the PDF file format. Adjust the CSS for the page to get the styling you want - see e.g. Creating Professional PDF Documents with CSS and Visualforce.
You will then need to encode that data as required by the "other application" and set the Content-Type header appropriately.