If you are not sure if the website you want to visit is safe, you can check it out here. Enter the address (url) of the website and see the invisible elements, such as a header or meta data.
site address:www.oreilly.com/catalog/hfobjects/chapter/ch03.pdf redirected to: www.oreilly.com/catalog/hfobjects/chapter/ch03.pd...
favicon.ico:
URL does not point to a web page (html/xhtml) or read error or page not found. (404)
Url ContentHyperText Markup Language (HTML)
MIME Type / Internet Media Typetext/html
MIME Type text
File Extension.html
More Details (link to:)Wikipedia: HTML
Powered by: Very Tiny URL Shortener at https://vturl.net VeryTinyURL

Header

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Server Apache
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Cache-Control max-age=2592000
Expires Sun, 19 Aug 2018 10:33:06 GMT
Date Fri, 20 Jul 2018 10:33:06 GMT
Connection keep-alive
HTTP/1.1 404 Not Found
Server Apache
Last-Modified Tue, 26 Sep 2017 21:45:20 GMT
Accept-Ranges bytes
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Content-Type text/html; charset=utf-8
Date Fri, 20 Jul 2018 10:33:07 GMT
Connection keep-alive

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name="target" content=""
name="twitter:title" content="Error (404)"
name="twitter:description" content=" "
name="twitter:site" content="@OReillyMedia"
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property="og:type" content="article"
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property="og:image" content="htt???/cdn.oreillystatic.com/oreilly/images/oreilly-social-icon-200.png"
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redirect count1
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* all occurrences of the string "http://" have been changed to "htt???/"