Unable to save pictures in combined PDF format

Hi there 

Hope you are doing well and sorry for the trouble you are experiencing while combining the photo files. 

Is this an issue with a particular image file or with all the files? Please try with different files and check.

Could you share the version of the Acrobat App and the OS you are using? A small video recording of the steps you are taking and the issue as it occurs would be very helpful for further investigation.

Also try updating the app to the latest version available on Play Store and reboot the device once and see if that works.

For future reference and self help please check the help page https://helpx.adobe.com/acrobat/mobile-app-faq.html