etherpad-lite: pdf import not working

Describe the bug When trying to import a pdf file into a pad, the following error message is displayed:

Import failed: We were not able to import this file. Please use a different document format or copy paste manually

import of other formats works. Export to pdf also works.

To Reproduce Steps to reproduce the behavior:

1. Go to ‘import/export’
2. Click on ‘choose file’
3. Select the file to import
4. Click on ‘import now’
5. See error

Expected behavior I would expect the contents of the pdf file to be imported into the pad.

Desktop (please complete the following information):

• OS: Client runs on MacOS 11.1, Etherpad 1.8.6 is deployed on Ubuntu 18.04.5 LTS
• Browser: Brave
• Version: 1.17.75 Chromium: 87.0.4280.88 (Official Build) (x86_64)

Additional context list of installed plugins: - ep_hash_auth - bcrypt - ep_comments_page - ep_headings2 - ep_align - ep_font_color - ep_table_of_contents - ep_font_family - ep_font_size - ep_image_upload - ep_embedded_hyperlinks2 - ep_set_title_on_pad - ep_print - ep_mammoth - argon2 - ep_draw

using LibreOffice (1:6.0.7) for conversion, also using Tidy (1:5.2.0-2)

The error message that is displayed in etherpad.log is:

[2020-12-18 13:45:20.019] [INFO] console - Exporting pad "dsfugauegfuoageh" in pdf format
[2020-12-18 13:45:20.020] [INFO] console - Found  undefined  for  dsfugauegfuoageh
[2020-12-18 13:45:35.888] [WARN] console - Converting Error: { [Error: ENOENT: no such file or directory, rename '/tmp/upload_f69452d349b913b2ea6766d70e14c6de.html' -> '/tmp/etherpad_import_635019763.html']
  errno: -2,
  code: 'ENOENT',
  syscall: 'rename',
  path: '/tmp/upload_f69452d349b913b2ea6766d70e14c6de.html',
  dest: '/tmp/etherpad_import_635019763.html' }
Error: ENOENT: no such file or directory, rename '/tmp/upload_f69452d349b913b2ea6766d70e14c6de.html' -> '/tmp/etherpad_import_635019763.html'
[2020-12-18 13:45:39.945] [INFO] access - [LEAVE] Pad "dsfugauegfuoageh": Author "a.wjkq3dh3PRzg9Ng9" on client YAh9_7m1mjNcFEawAAAD with IP "ANONYMOUS" left the pad