As expected that PDF renders fine for me on Chrome 56.0.2924.3 Linux and Chrome 54.0.2840.99 Windows.  Definitely sounds like some sort of font issue.  Dan?

I figured it would.  I was told I should report the issue here, and I agreed since it does render properly for me in other browsers.

Does the pdf still render improperly from you when you open it in incognito mode? AFAIK Pdfium does not fill unknown characters with blocks, it leaves blanks...

Yes, it renders improperly even in Incognito mode.

Unable to reproduce the issue on Win 10,Mac 10.11.6 & Ubuntu 14.04 using stable 54.0.2840.98/99/100 and canary 57.0.2937.0.

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My Chrome just updated to Version 55.0.2883.75 m (64-bit) and it's still showing the squares as I've detailed above.

I've just downloaded the PDF Viewer extension for Chrome (https://chrome.google.com/webstore/detail/pdf-viewer/oemmndcbldboiebfnladdacbdfmadadm) and tried viewing the same PDF document.  It seems to work perfectly fine as you can see in the attached screenshot.  Chrome's built-in viewer does not properly display it, but the extension working inside Chrome does.

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I have the same problem. Reading the above mirrors exactly my experience and observations. 

As an additional data point... I have 3 PCs. Two are (older) Win 8 that are upgraded to Win 10, Chrome displays PDFs correctly. The third is newer that came with Win 10, Chrome does NOT properly display PDFs. 

Sorry if this is just noise. In my software career I have found stranger things that have caused weirder issues. 

Since I cannot reproduce the problem here, it is hard to investigate what is going on. The PDF uses ArialMT but it is not embedded, so we find a substitute font. Maybe in your computer we are using as substitute a strange font which only contains upper case letters? This could happen if you have added the font to the font directory in your computer.

Is there any way for me to know what font it's using as the substitute?  I've gone through most of the installed fonts in Control Panel and haven't found any that display the way they do in my screenshots.  Perhaps knowing what it's using as a substitute will help me find out whether it's a corrupt font or not, and then I can report back here.

There are ways but I can't think of anything easy :( One way is to get a chrome build in your pc, add a few lines of code, and  open up the file using that build  (I'm assuming you don't want to do that so I went over it without details). Another way is to search by iterating: move some fonts out of the font directory (into some other directory outside of that), go to Chrome and open the file to see how it looks, repeat. For instance, if you move out all fonts except Arial, the lowercase letters should show up, otherwise there could be some other problem.

I'm not afraid of getting my hands dirty :)  As for moving fonts out of the font directory, would that not invalidate any fonts used by the OS?

Ok, maybe that was not a good example. You could remove just Arial and see if there is some change. Or you could take a look and see if you have typefaces other than those that already come with Windows: https://en.wikipedia.org/wiki/List_of_typefaces_included_with_Microsoft_Windows

I tried hiding Arial, to no avail.  I did just go through every one of my fonts in the Character Map and they all seem to display fine, no missing lowercase letters, etc.

You mentioned having added fonts to my font directory.  I do play a lot of flight simulators, which sometimes require fonts to be installed for realism on the various displays.  There are indeed many fonts in that font folder that come from installing many of the aircraft that require such a thing.  However, even those fonts display fine.  I am unsure as to how those very niche fonts would get assigned/mapped as a substitute before something like Arial or Segoe UI, etc.

Ok, thank you for your input! I'm kind of clueless as to what may be the issue, so some questions:
*Do the bold lowercase letters in the doc have a problem as well?
*Have you tried reinstalling / resetting Chrome to its default settings?
One thing you can also try is to run an older version of Chrome and see if the pdf still renders incorrectly.

The bold lowercase letters do display just fine, which I noticed.  I've tried resetting Chrome, un/reinstalling it, and as I said at some point earlier, I even moved my profile's folder (Default) out to let Chrome create a new one, thinking maybe that would help.

I don't know why Chrome wouldn't display those characters correctly when even the PDF Reader extension running inside Chrome displays them just fine.  I'd assume it would use the same substitute font(s) if necessary.  I don't have any issue when viewing any webpage, either.  It's only in the built-in PDF viewer.

Is this still a problem for you? I think we never figure out a possible cause and it seems to be a problem in your machine, but maybe it magically fixed itself.

Yes, it's still an issue for me.  It hasn't magically fixed itself unfortunately.  I'm still using the PDF Viewer extension I mentioned several comments above, and it's still working perfectly fine, so perhaps I'll just stick with that.

drott@, any idea off the top of your head of what could be causing this? My understanding is that on Windows we use bundled freetype, so that plus having some standard fonts would be enough to render this PDF properly. Otherwise, I'm going to close as WontFix since it seems to be a bug unique to the reporter's system.

I can contribute only some speculation:

It look like an issue with fallback, comment #10 - if really facing the identical problem - indicates that  a font from Windows 8, which remained on the system through the upgrade to Windows 10 might be used and working, whereas in clean Win 10 machine the default set fonts produces the failed case?

Or: An issue with bitmap glyphs in the font. The section of the PDF which exposes the missing lowercase glyphs specifies "Calibri". 

Clorix1@, could you try hiding the Calibri font family from Windows, by moving it out from your font folder? What happens if you do that?

Calibri has bitmaps glyphs at certain sizes 13,15-17 and 19ppem I believe, maybe PDFium has issues with displaying these correctly, and then fails to do further fallback?

I wasn't able to move the Calibri font out of the Fonts folder, so I instead right clicked it and then chose Hide.  Hopefully that would have the same effect.

Unfortunately, the documents I checked still had the squares all over it as I originally described.  If there is anything else I can do to check it, let me know and I'd be happy to try it out for you.

Unfortunately I can't think of anything else and cannot debug without being able to reproduce. This seems to be a problem specific to your system fonts, PDFium font code, and Freetype not playing along well.

I hate to re-open this issue as it has already been marked as "Won't Fix" but I just found something new that could perhaps help identify the issue.

I've just updated to Chrome Version 60.0.3112.78 (Official Build) (64-bit) and tried the built-in PDF viewer on a whim and the view has changed a bit (I don't know which earlier version would have caused this change, however, since I haven't checked the built-in PDF viewer since this was marked as Won't Fix).

In the first attachment to this post, you can see I've tried the same document as when I first reported this issue, though now instead of squares being displayed, there is nothing.

I have found a document which seems to appear correctly in its entirety, as you can see in the second attachment.  This document also contains bold type and of course lowercase letters.

I have since updated my Windows 10 installation to the Creators Update (within the past month and a half or so), but I don't know if that has anything to do with the change in the way the PDFs are being displayed.

If nothing new is able to be learned from this, then I'll just go about my business using the PDF Viewer extension I've been using for several months now, which still works just fine.  So it isn't a big deal for me, though it might be for someone else, so I thought I'd report my findings.

Thanks for looking into it!

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It looks like the encoding being used by PDFium is just wrong, since even the letters that show up sometimes don't match what the letters in the correct rendering should be. That's strange, the encodings used in the PDF are Identity-H and WinAnsiEncoding, which are pretty standard. It's hard for me to speculate what could be the problem without being able to reproduce, sorry...