Запустите .reg файл:
Код:

Windows Registry Editor Version 5.00
[-HKEY_CLASSES_ROOT\.pdf]
[HKEY_CLASSES_ROOT\.pdf]
"Content Type"="application/pdf"
[HKEY_CLASSES_ROOT\.pdf\OpenWithList]
[HKEY_CLASSES_ROOT\.pdf\OpenWithProgids]
"AppXd4nrz8ff68srnhf9t5a8sbjyar1cr723"=hex(0):
[HKEY_CLASSES_ROOT\.pdf\PersistentHandler]
@="{1AA9BF05-9A97-48c1-BA28-D9DCE795E93C}"
[-HKEY_CLASSES_ROOT\SystemFileAssociations\.pdf]
[-HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.pdf]
[HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.pdf\OpenWithList]
[HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.pdf\UserChoice]
"Hash"="AD8mJSYO9c0="
"ProgId"="AppXd4nrz8ff68srnhf9t5a8sbjyar1cr723"
[-HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\Roaming\OpenWith\FileExts\.pdf]
[HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\Roaming\OpenWith\FileExts\.pdf\UserChoice]
"Hash"="/pcHLCV4T1E="
"ProgId"="AppXd4nrz8ff68srnhf9t5a8sbjyar1cr723"
Затем назначьте приложение, которое вы хотите, любым из следующих способов -
Default Apps - Choose in Windows 10