Auto Tag in Acrobat Pro DC removes curly braces and square brackets from mathematical equations

Hello @Santosh,

I hope you are doing well, and thanks for reaching out. We're sorry for the trouble you had.

Could you please share more details about the issue?

1. Which OS/version are you using: Windows 10/11 or macOS?

2. How was the PDF created: Word/PDFMaker, InDesign, scanned/OCR, or another tool?

3. Is cloud-based auto-tagging enabled in Acrobat, or are you using the local/legacy tagging method?

Please note that Acrobat's autotag targets headings, paragraphs, lists, tables, and reading order. Pre-PDF 2.0, PDF has no native math semantics, so equations have to be handled specially (a Formula tag with alternate text, or MathML), not by raw-glyph autotagging.

The likely root cause, which is also your question 4 (font encoding / ToUnicode). This is the most probable explanation: the brace and bracket glyphs in your equations likely lack proper Unicode/ToUnicode mappings. A PDF font has a glyph table (shapes used to draw the page) and a ToUnicode map (what character each glyph represents). When a glyph has no valid Unicode mapping, it still renders and prints fine, but Acrobat does not know what character it is, so a tagging or text-recognition pass can drop it. Math fonts from LaTeX and MathType are especially prone to this, particularly large "stretchy" braces and brackets that are assembled from glyph pieces or live in symbol/private-use encodings. Those are exactly the characters most likely to be omitted.

Are the braces and brackets missing from the visible/printed page, or only from the Tags panel, Content panel, and extracted (copy-paste) text?

Before running autotag, copy-paste one of the equations, or Save As Text, and see whether the braces already come out wrong. If they are already missing or garbled before autotag, the source PDF's font encoding is the cause. If they copy correctly before autotag but disappear from the visible page after, then can you share the PDF file with us for testing purposes?

Suggestions:

In Acrobat: after tagging, manually wrap each equation in a Formula tag and add Alternate Text (or Actual Text) that spells out the full expression, including the grouping symbols. Where an equation is effectively an image, tag it as a Figure with equivalent alt text. Use All tools > Prepare for accessibility > Fix reading order and the Tags panel (right-click the tag > Properties) to set the Formula tag and alt text.

Please note that autotag overwrites existing tags and can strip alt text, so keep a copy before running it, and prefer manual Formula tagging over re-running autotag on math-heavy files.

You can also refer to these Adobe articles and try the suggestions:

https://adobe.ly/3Rzfz5s

https://adobe.ly/4gNy3cR

https://adobe.ly/4pARJmo

Let us know how it goes, and please reach out for any assistance.

Regards,

Anand Sri.