PDF is not meant for editing. They might be able to make changes or adjustments to the file, but I would be skeptical if they claimed they do this often and it's "no problem". Editing PDFs is usually a last resort sort of thing. If you want to give them a file that's good quality and can be edited, then you should ignore any issues about file size. Everything is a compromise. All a file can ever be is data. If you want a smaller file, then you must remove data. If you remove data, you are sending them less file than they might need or you want to send. It's OK to try to trim a few MB here or there. Linking, rather than embedding images is one way. Saving as AI file without PDF compatibility is another. I actually really like that one, since it forces them to use the Illustrator file, not the embedded PDF. Remember to send linked files, too. If you outline fonts, then no need to send fonts or worry about font licensing issues, but then, forget about making type corrections without sending a new file. Put all files in one folder and ZIP that folder, then send that ZIP file. If it's too big for email, then use FTP or other file sharing services.
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