Critical bug: Fill & Sign text becomes invisible when entering Cyrillic characters in Acrobat Reader

Hello Adobe Support Team,

I would like to report a reproducible bug in Adobe Acrobat Reader for Windows.

The problem occurs specifically when using:

Fill & Sign → Add Text

Problem

When I enter text using a Cyrillic keyboard layout (Ukrainian or Russian), the text becomes completely invisible.

The text is actually entered and remains present in the document — it can be selected and copied successfully — but it is not rendered visibly on the screen.

There is a very specific and reproducible behavior:

1. Open any PDF.
2. Select Fill & Sign → Add Text.
3. Start typing in English — the text is visible.
4. Switch the Windows keyboard layout to Ukrainian or Russian.
5. Type Cyrillic characters.
6. The Cyrillic text becomes invisible.
7. After this happens, even the previously visible English text becomes invisible.
8. Copying the invisible text with Ctrl+C and pasting it into Notepad or Word works correctly, proving that the text itself is present and correctly encoded.

The same problem occurs if Acrobat is started while the Windows keyboard is already set to Ukrainian/Russian: Cyrillic text is immediately invisible.

Important troubleshooting already performed

I have spent considerable time troubleshooting this issue:

• Completely uninstalled Adobe Acrobat Reader.
• Used Adobe's cleaning/removal procedure.
• Removed Adobe-related application data and caches.
• Reinstalled the latest official version of Adobe Acrobat Reader.
• Tested multiple PDF files — the problem is not specific to one PDF.
• Tested different text colors — the problem remains.
• Tested different fonts available in Windows, including Consolas.
• Verified that Consolas contains Cyrillic characters and all four font styles are installed.
• Tested Windows text input in Notepad — Ukrainian, Russian and English work normally.
• Tested text copying from Acrobat — the invisible text copies correctly.
• Deleted AdobeSysFnt26.lst. This temporarily restores normal rendering, but the problem returns later.
• Changed Acrobat text-rendering/anti-aliasing settings — no effect.
• The problem persists after a completely clean installation.
• Most importantly, I replaced the entire computer with different hardware, and the exact same problem returned after approximately one day.

Therefore, the problem is not related to the original computer, CPU, GPU or its drivers.

Current environment

Application: Adobe Acrobat Reader
Version: 2026.001.21771
Operating system: Windows 10
Architecture: 64-bit
Input languages: English, Ukrainian, Russian
Feature affected: Fill & Sign → Add Text

Additional observation

The file AdobeSysFnt26.lst appears to be involved in the problem.

Deleting this file causes Acrobat to rebuild its font cache and temporarily restores correct text rendering. However, after the problem returns, the same invisible-text behavior occurs again.

I would therefore strongly suspect a bug in the font handling/rendering mechanism used by Fill & Sign, particularly when Acrobat processes Cyrillic characters.

Request

Could you please escalate this issue to the Acrobat engineering team and confirm whether this is a known bug?

I would appreciate:

1. Confirmation that the issue has been logged as a software bug.
2. A workaround that does not require repeatedly deleting AdobeSysFnt26.lst.
3. If possible, a fixed version or hotfix.
4. Information about whether Adobe can provide a diagnostic build or logging procedure that would help your engineers reproduce the problem.

I can provide screenshots, the affected AdobeSysFnt26.lst file, system information, and a screen recording demonstrating the exact sequence that reproduces the problem.

This issue is particularly disruptive because the affected computer is used for daily work with many PDF documents, and the Fill & Sign → Add Text functionality is required for our workflow.

Thank you. I would appreciate it if this could be escalated to the Acrobat engineering team.

Best regards,
Dmytro