Once i upload a file and send the link is it permanent? So if i upload user manuals and use that link to send to customers can i trust that it will always be there and open that file or does it disapear after so many days?
The files will be there unless you delete them manually. For more detailed information, you can refer to Adobe Send & Track FAQ Link: https://helpx.adobe.com/document-cloud/faq/adobe-send-faq.html
The link generated when you upload the file to share is for one-time use, but the file is uploaded to your account and can be accessed from https://cloud.acrobat.com/sentfiles
Feel free to update this discussion for any further assistance.