To import a picture/image into a PDF, you would need a PDF editor (not a PDF viewer) like Acrobat Pro DC.
Unfortunately, it is not possible to perform the operation with the mobile or desktop version of Reader.
You can install a free 30-day trial version of Acrobat Pro DC on your Windows or Mac desktop computer to see if it fits your needs.
Another option is to covert (not import) an image (supported formats: .bmp, .gif, .jpeg, .jpg, .png, .tif, .tiff) to a single-page PDF document using the "Camera to PDF" feature.
it requires the subscription to the Adobe PDF Pack service.
The "Camera to PDF" feature is available in Acrobat Reader for iOS (mobile app), but not Acrobat Reader for Android.
Sorry...neither one may be feasible to you if you are looking for a free option.
Please let us know if you have additional questions.