how do i create a border around iframe?

If you want to use inline HTML styling:

 <iframe src="https://link_to_my_file/file.pdf"     style="width:1000px; height:300px; border: 1px solid black;"></iframe>

html css wordpress iframe border

The out put will not work in the snippet.Attribute which are deprecated in HTML5 for <iframe>

scrolling

frameborder

align

longdesc

marginwidth

instead of using these as iframe inline attribute you can use it in css

DEMO:

iframe{border:4px solid red;}

<iframe src="https://www.google.co.in/?gfe_rd=cr&dcr=0&ei=WyV_WvDBOY_E8wfHmba4Aw"></iframe>