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I am troubleshooting a problem with opening PDFs from websites so I uninstalled Adobe Reader. Out of curiosity I checked whether I could still open PDFs from websites (here is a random example). Surprisingly I could still open PDFs from both Chrome (my preferred browser) and Internet Explorer. I believe IE is using Edge to open the PDFs but the PDF interface looks different in Chrome, so it might be another application. Unfortunately I can't uninstall Edge to check. How can I figure out what application Chrome is using to open PDFs from websites?

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    Chrome has a built-in PDF viewer, Microsoft Edge also has a built-in PDF viewer. You should be able to type "chrome://plugins" in your Chrome URL bar and see what's installed. – Andrew Nov 27 '18 at 20:39
  • I get ERR_INVALID_URL when I type chrome://plugins in my URL bar, unfortunately. – KAE Nov 27 '18 at 20:57
  • Use chrome://settings/content to control when Adobe Flash content is displayed and chrome://components to display the version of Adobe Flash Player installed. Source: howtogeek.com/303934/… – absenthecon Nov 28 '18 at 5:14
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    all the major browsers nowadays have their built-in PDF readers – phuclv Nov 28 '18 at 15:32
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    @Andrew, there is currently no chrome url chrome://plugins as you mentioned – KumarAnkit Nov 29 '18 at 7:54
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Chrome itself is the application that is viewing the PDFs.

Windows 10 Edge can also open PDFs directly. Please note, IE is an older, separate application from Edge. If your users start in IE, they will not be able to open PDFs directly in IE unless they have Adobe plugin installed.

Firefox is able to view PDFs without a plugin : https://support.mozilla.org/en-US/kb/view-pdf-files-firefox .

Some websites (bank websites in my experience) will force a download rather than allowing it to be opened in the same browser. In Firefox, I was able to sometimes change the behavior by changing the MIME settings, but it didn't work consistently. https://support.mozilla.org/en-US/kb/change-firefox-behavior-when-open-file

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    "Windows 10 Edge can also open PDFs directly." Might be worth pointing out that Edge can also open EPUB files, and it does a really good job at it. – walen Nov 28 '18 at 8:40
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    @LuisG. Edge and compliments about its performance isn't something I see very often. Is it actually good at EPUB or are you making fun of it? – Azor Ahai Nov 28 '18 at 19:03
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    @AzorAhai, EPUB as it's actually used is basically structured HTML. I don't see why Edge would have trouble with it, if it's programed to understand the packaging. – Mark Nov 28 '18 at 22:20
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    Note that even if the browser downloads the file because of the download headers, you can still just drag and drop the file into the browser (or use File->Open) and open the PDF file manually – SztupY Nov 29 '18 at 8:21
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    @AzorAhai I'm being serious. I've seen Edge laugh in the face of Calibre or Adobe Digital Editions after they made a mess of some weird EPUBs that Edge could show (almost) flawlessly. Example: Calibre; ADE; Edge. – walen Nov 29 '18 at 9:51
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From memory, Google Chrome uses a built in PDF viewer which was written in JavaScript I believe C++, thanks to the helpful reminder in the comments :)

This comes bundled with Chrome by default.

For me, I can view some of the related JavaScript here:

chrome-extension://mhjfbmdgcfjbbpaeojofohoefgiehjai/pdf_viewer.js

You can view some related code by opening the Chrome DevTools on the PDF Viewer.

Firefox uses another similar approach, again, written in JavaScript, although their documentation is more publicly available & from memory, is encouraged for others to use to display PDFs on their website.

Read more about Firefox's implementation here: PDF.js by Mozilla

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    It's written in C++, source code available here – Paddy Nov 28 '18 at 8:53
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As the chrome is derived from the chromium open-source project, it also uses the same embedded pdf-viewer that is shipped with Chromium Browser. So when a pdf file is encountered, chrome tries to open it using this pdf viewer.

If you open the

chrome://system

you would notice that it shows the open tabs and running extentions, but it does not shows any info about pdf viewer it is using here.

But when I open this

chrome://local-state

chrome shows multiple pdf plugin components including Adobe Reader and Chromium PDF reader. It might differ in your system.

The Readme docs are available for the chromium project, but I could not find the docs for pdf viewer. You can read it here

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