Therein lies the rub. If a PDF has DRM infesting it then you cannot reformat it in any way, including adjusting margins.
PDF's are documents not ebooks. Publishers do not create a PDF document with an ebook reader in mind and ebook manufacturers such as Kobo would not consider a PDF to be as important as say an ePUB to display.
The only option you have, apart from seeking an ePUB version, is to remove the DRM.