As per the issue description, you are getting the popup/flash window everytime you open a PDF/Reader.
The First Time Experience (FTE) feature displays help content and tips when the application is started.
Assuming you are using a Windows machine, to disable FTE, set the registry value :
Open registry through Run command i.e. type regedit in Run and click ok.
1. Navigate to the Registry location: HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Adobe\Acrobat Reader\DC\FeatureLockDown.
2. Highlight FeatureLockDown.
3. In the right window, right click in the Blank space and choose New > DWORD (32 bit) Value.
4. Enter the value bToggleFTE
5. Highlight the Registry value i.e. bToggleFTE > Right click and choose Modify.
6. Enter Value Data as 1 and click Ok.
Reboot the computer and launch the Reader.
Please keep us posted with the results.
Thank you, both, for the reply! no more pop ups after the change to the registry.
Please share the following information:
1. Adobe Reader version
2. Machine configuration (win or mac)
It would be also helpful if you can share a video showing the issue.