[FOP-2701] Some of the latin ligatures make text not searchable in PDF

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.1
• Component/s: font/opentype
• Environment: Windows 10, Calibri font.
• Flags: Important
• Assignee: Unassigned
• Reporter: Dan Caprioara
• Created: 04/Apr/17 06:14
• Updated: 08/Jun/22 13:16

Description

This problem happens using the Calibri font, that is packed in the MS Office suite and Windows 10.

I tested with the following text: file settings.
The resulted PDF text contains ligatures: (fi)le se(tti)ngs

Searching for file in Acrobat Reader results in the first word being selected. This is Ok. But searching for set, or settings gives no results.

The same example, run with Antenna House works fine, you get results when searching for settings.

Here is the complete FO file:

<?xml version="1.0" encoding="UTF-8"?>
<fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format">
    <fo:layout-master-set>
        <fo:simple-page-master master-name="a">
            <fo:region-body/>
        </fo:simple-page-master>
    </fo:layout-master-set>
    <fo:page-sequence master-reference="a">
        <fo:flow flow-name="xsl-region-body">
            <fo:block font-family="Calibri" font-size="40pt">file settings</fo:block>
        </fo:flow>
    </fo:page-sequence>
</fo:root>

Some considerations:

1. A workaround would be to reject all the substitutions that are not part of org.apache.fop.fonts.type1.AdobeStandardEncoding. This would leave the (fi) ligature, but reject the (tti) one. But this seems to work only for Calibri and not for Roboto!!
2. I think there might be some issues with the font embedding, and some substitution mapping data is lost. It is just a guess, I am not sure how PDF deals with substitutions.

I know that setting in FO xml:lang to "en" disables the ligatures, but is not a solution for my project. I would appreciate any suggestions.