How to crop a PDF
Open your PDF and drag a box over the area you want to keep. Choose whether the box applies to this page, every page, or only odd or even pages, which is handy for scanned books where left and right pages have different margins. Press Use this box, check the thumbnails, and download.
Trim white margins automatically
Trim white margins draws each page, finds where the text and pictures start and end, and crops to that area with a small margin you can set. It works page by page, so pages with different layouts each get their own crop. It is ideal for reading papers and slides on a phone or e-reader.
What cropping changes
Cropping changes the visible area of each page by setting its crop box and media box. The content outside the box is hidden rather than deleted, so the file stays sharp and its text stays searchable. If you need to remove something for good, use a redaction tool instead.