BUG - Commenting PDFs empties or shrinks the PDF

[jprusch]

Summary

Commenting an attached PDF file either clears the PDF or shrinks them to a quarter size

Steps To Reproduce

Steps to reproduce the behavior:

1. Attach a PDF to a channel
2. Click on 'comment'
3. Write a comment & close the PDF viewer
4. Open PDF again

Expected behavior

PDF is the same as before with comment

Observed Behavior (that appears unintentional)

PDF is either empty or a quarter of the size with comment displayes

Screenshots

See attached mp4 for two examples

Environment

• Mattermost version: 5.38.2
• OS: Windows 10
• Platform: Browser & Desktop
• Browser (if applicable): Chrome 93
• Desktop: 4.7.1

pdf_quarter_size.mp4

pdf_empty_comment.mp4