This article helps how to send files from Mac to WhatsApp on BlueStacks app player:
Follow the steps mentioned in the URL below to import files from Mac to BlueStacks:
Follow steps 1 to 9 as mentioned in the above URL. Please make sure you select "WhatsApp" folder in step 10.
Go to 'Media'.
Tap on 'Whatsapp images' and 'OK' (If the media files you have imported are videos, audios select the folders accordingly).
Now, launch WhatsApp application on the app player. Select a contact to whom you want to send an image. Click on the 'attachment' icon and select Gallery option to send an image (for other media you may use video, audio etc accordingly).
Files imported in step (1) will be visible here. Select the file to send it to your contact.