Hi Everyone,
As a retired U.S. expat, I had some pretty big files to upload for proof of assets and domicile, not to mention the I-864 itself! After wrestling with the subject for half a day, I stumbled across a relatively easy solution to reducing the files to fit the 4 mb uploading restriction.
I have the HP Smart app downloaded on my computer to use with my HP printer. In the app, it says: "HP Smart can use the camera in your computer, if available, to scan documents or photos. You can also import files stored on your computer and convert them to PDFs." Please note that, for this purpose, the app only works on a computer (not cellphone). YOU DO NOT NEED AN HP PRINTER TO USE THIS FUNCTION.
You do need to have each page of your documents saved on your computer as JPG files. You can do this in any number of ways, such as scanning as your documents as jpg's with your phone or scanner, or converting files with an app (I used the Combine PDF File extension on Chrome which works with files locally and not on the Cloud).
In the HP Smart app, go to SCAN, and do the following:
IMPORT-(choose .jpg document & choose FULL to scan entire page)-APPLY-Add additional pages by clicking the + sign.
When you have all your pages scanned: SAVE-COMPRESSION-HIGH-SAVE-Save file to Folder.
With this method, I managed to reduce one file from 4745 kbs to 745 kbs and the other from 8173 kbs to 1998 kbs.
Hopefully this will help the rest of you with this tricky subject. Good luck!