PDF24 Blacken: redacted OCR PDF incompatible with some PDF readers

Hi,

I've got several PDF-Files originating from commercial scan systems internally using ABBY FineReader Engine 11. Files are PDF 1.5 ("Acrobat 6.x") and contain the scanned image (JBIG2) on top of an "invisible" OCR-Text (FlateDecode). Additionally two Fonts are embedded.

Opening the file in PDF24 Blacken works as expected, I can draw shapes and save the file without any indication of an error. The resulting file can be opened in Adobe Reader (2022.001.20169, 2022.002.20191), however viewing a page containing blackened parts leads to an error message and empty page displayed:

An error exists on this page. Acrobat may not display the page correctly. Please contact the person who created the PDF document to correct the problem.

I could reproduce the same problem with older systems (PDF 1.3, Adobe 4.x, also ABBY FineReader Engine 11). Opening the blackened file works in some 3rd party readers (PDF24 Reader, xpdf), others show the page but also errors (pdftopng) or also only a blank page (atril).

Source File details:

Creator: Streamline NX
Producer: ABBYY FineReader Engine 11
CreationDate: Thu Feb 17 17:10:52 2022 CET
ModDate: Thu Feb 17 17:10:52 2022 CET
Custom Metadata: no
Metadata Stream: no
Tagged: no
UserProperties: no
Suspects: no
Form: none
JavaScript: no
Pages: 1
Encrypted: no
Page size: 595.2 x 841.9 pts (A4)
Page rot: 0
File size: 15780 bytes
Optimized: no
PDF version: 1.5

Blackend file pdftopng errors:

Syntax Error: XObject 'Bg' is unknown
Syntax Error: XObject 'PDF24-1' is unknown
Syntax Error (1080): Unknown operator 'Qq'
Syntax Error: Couldn't find a font for 'Arial-BoldItalicMT'
Syntax Error: Couldn't find a font for 'Arial-BoldItalicMT'
Syntax Error: Couldn't find a font for 'Arial-ItalicMT'
Syntax Error: Couldn't find a font for 'Arial-ItalicMT'

Example files can be provided.