PDF file cannot be opened when installing Observer on iPad Air1 (mobile terminal 1.41) (iOS system version 12.5.6)

Mobile
1

PDF files cannot be opened when installing Obsidian (mobile terminal 1.41) (multiple PDF files are attempted, all fail)

Expected effect
Subsequent versions can open PDF files and browse

1
11706×1280 117 KB

environment
Operating system: ios 12.5.6
Equipment: iPad Air1 (A7 processor released in 2013)

IOS12.5.6
IOS12.5.61706×1280 162 KB

Solution Attempted
After borrowing someone else’s iPad Air5 to install the Obsidian (mobile terminal 1.41), you can open the PDF file system version IOS 15.6.1 (M1 processor)

3
3863×1920 151 KB