i need this plugin.

i need a plugin to do that:

im going to start shareware site using wordpress.
i want a plugin that create afield “textbox” in writing post that i can past download link.
and this link appears to visitors as ” Download Now”.

EX:
in my WP dashboard im writing new post about kaspersky ,
i want afield to past download link https://kaspersky.com/kasperdownload.rar

for visitors :
after reading the post they can see Download Now which they can download that shareware.

“Download Now” word is fixable in all post but the changeable is software links.

i want it to be :

<a href="changeable links that i can add when writing posts" target="blank">Download Now "which should to be fixable in posts before comments"</a>