shrink a file, for example, from 100 Mb with acrobat reader,

Hi Berdonvi

We are sorry for the trouble. As described the application closes at the end of the process when reducing the file size With Acrobat Reader

Adobe Acrobat Reader is a freeware application with limited functionalities. It is used for viewing, printing, signing, sharing, and annotating PDFs. We can not reduce the file size with the freeware application.

Are you you referring to Adobe Acrobat DC? If yes, we tried to reproduce the issue and its working fine on our end.

We need some more information for a better understanding:

• Is this a behavior with a particular PDF file or with all the PDFs that you try to reduce the file size? Please try with a different PDF file and check. If its a file specific issue please share the file with us for testing. Upload the file to the document cloud (https://documentcloud.adobe.com/link/home/) generate the link and share it with us.
• What is the workflow/steps you are doing to reduce the file size?
• What is the version of the Adobe Acrobat DC you are using?To check the version go to Help > About Adobe Acrobat DC
  Make sure you have the latest version 20.006.20042 installed. Go to Help > Check for Updates

Please try to reboot the computer and check again, You may also try to repair the installation (For Windows Only) Go to Help > Repair Installation and see if that works.

If it still doesn't work,  please try the steps below  and see if that helps

• Remove the application using the Acrobat Cleaner Tool (https://labs.adobe.com/downloads/acrobatcleaner.html)
• Reboot the computer
• Reinstall the application using the link (https://helpx.adobe.com/in/download-install/kb/acrobat-downloads.html)

Let us know how it goes

Regards

Amal