Is there a way to increase the font size on a Windows Help file (CHM file) with recent versions of Internet Explorer? You used to be able to, but I think after IE7 the option was removed from the UI.


The problem is that newer versions of ie removed the "Text Size" feature in favor of a "zoom" ability (which scales images along with text).

The ie context menu doesn't include an option for "zoom", as it did for "text size". There is a way to fudge the font sizes in the embedded browser used by the CHM reader.

Internet Explorer has an accessibility option to ignore font-sizes changes. This is meant to allow fonts to stay readable, when web-sites try to use a smaller font.

alt text

Turning this option on will make text in the HtmlHelp viewer the default sized font; and easy to read.

But the actual answer to your question is: There is no way to adjust the font size in Microsoft's HtmlHelp reader You can use:

  • Ctrl++ to zoom in
  • Ctrl+- to zoom out
  • Ctrl+0 to reset to default zoom

(tested in Windows 10)

  • 10x a lot man! Your solution works like a charm.
    – Soonts
    Oct 22 '11 at 14:51

I'm a bookworm and some eBooks come as CHM, so no longer being able to change the font size was most annoying. Since then I'm using HelpExplorer.

enter image description here

There is a little problem though. The program is shareware but you can't really pay for it since the company seems to have vanished from the face of the earth and all links are dead. However, it does the job and I'm quite happy with it.


I just found that increasing the text size in IE, and then reopening the CHM document increases the font size within the CHM document.


I use HTML Help workshop to decompile the CHM, modify the HTML/CSS, and then compile it back to CHM. I know this is a little annoying, but it fixes the problem.

Or, you can use KchmViewer, which allows you to change font size.

The problem with Kchmviewer is that it only allows you to in/decrease fonts that are not specifically set by stylesheets or font tags in the source of those pages. So sometimes it is pretty useless to only increase the size of the titles for example.


Official chm reader in windows doesn't have this feature in it's options but options for ie8 effected chm reader .

  • also you can use Firefox plug in that read chm file in Firefox Aug 28 '09 at 20:34
  • 1
    +1 but official reader has this feature.
    – Am1rr3zA
    Aug 28 '09 at 20:49

Actually just like in IE, Ctrl++, Ctrl+-, and Ctrl+0 still work as "zoom" hot keys, even though this is not apparent in the UI.

(I've tried to update the popular answer to clarify this.)


I think it's an option the creator of the CHM specifies. In an old job we used to supply our help files as CHM (among other formats) and I'm sure that there was an option we had to set to get the "change font size" on the toolbar.

I've just opened one of the files and the option's still there and it works. Unfortunately I don't have access to the tool we used at the moment so I can't check.


You may create a CSS file defining desired font size and specify it in Internet Explorer properties: Styling -> Use user-defined style-sheets.

    font-size: 30px;

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