Acrobat Reader hangs on keyboard-layout switch (Alt+Shift) while a form field has focus

Product: Adobe Acrobat Reader (64-bit) 26.002.22031 (file version 26.2.22031.0)
OS: Windows 11 Pro, builds 10.0.26200 and 10.0.26300 (reproduced on both)
Input languages: English (United States) 0409 + Greek 0408, switch hotkey Left Alt+Shift

Summary

With the caret in a text field of an AcroForm, switching the keyboard layout with Alt+Shift makes
Reader stop responding permanently (window "Not responding", must be killed). It happens on the
first layout switch: the layout changes once, then the UI thread hangs.

It depends only on the page content under the form, not on the fields: the same page with one
field hangs, and the same 40 fields on a blank page never hang.

Steps to reproduce

1. Open repro_FREEZES.pdf in Acrobat Reader.
2. Click on the page, press Tab so a text field gets the caret.
3. Hold Left Alt and press Shift several times (EN ↔ EL).

Actual: Reader hangs after the first switch and never recovers.
Expected: layout switches, Reader stays responsive (as with repro_OK_control.pdf).

Attached files

| File | Result (automated runs) |
|---|---|
| repro_FREEZES.pdf | hung 3/3 |
| repro_OK_control.pdf | hung 0/10 |

The two files have the same 40 form fields, the same resources, and the same drawing: one text line
and one stroked line. Their page content streams differ in only two ways:
- repro_FREEZES.pdf has 115 extra operators after the line: 111 rg/RG colour operators, plus
2 w and 2 n. None of them paint anything, because no drawing operator follows them.
- repro_FREEZES.pdf lacks one empty text object, BT /F1 12 Tf 14.4 TL ET, which shows no text.

In separate tests the extra w/n operators alone did not cause the hang (0/10).

Findings (automated test harness, SendInput + hang detection, Reader restarted every run)

• The real form hung 15/15 (v1.21) and 3/3 (v1.22); a one-field test PDF never hung (0/15).
• Not the cause (each tested): NeedAppearances, field JavaScript, doNotSpellCheck, field fonts, combo boxes, transparency, images, number of fields, tagged PDF / StructTreeRoot, character spacing (Tc), bold/oblique fonts, non-ASCII characters.
• Needs text and paths and many colour state changes on the same page:
  • text only (47 colour changes): 0/11
  • paths only (35 colour changes): 0/11
  • text + line + 55 interleaved colour ops: 1/10
  • text + line + 111 interleaved colour ops: 3/3
  • text + line + 111 × the same colour: 0/10
• Moving the page content into Form XObjects (one, or text and paths separately) still hangs (3/3).
• A page with no content of its own does not hang: the same drawing placed as the appearance of a read-only Stamp annotation hung 0/10, rasterised to an image also 0/10.

Workaround used

Page content moved into the /N appearance stream of a locked, read-only, printable Stamp annotation
covering the page; page /Contents left empty. Appearance is identical, and the freeze no longer occurs.