After I inserted an image to Libreoffice Writer and cropped it, I exported the document to pdf. But the image in the pdf file is not cropped correctly. You can download a sample document on google drive. I am using Libreoffice 5.3.4 on Manjaro Linux.
EDIT: same result in Libreoffice Impress
EDIT2:
How I cropped the image:
- Open a new document in Writer
- Click Insert > Image… to insert the image
- Right click on the image and click Crop
- Crop the black region on the right and left like this
- Save the document and export to pdf
- Open the pdf, and some black region is on the right and left(although it is much smaller than the original image)