This tool cuts away the edges of PDF pages. Type how many millimetres to remove from the top, bottom, left and right, or draw the area you want to keep directly on the page preview: drag to draw a box, drag it to move it, and pull a corner to resize it. Detect white margins looks at the current page and fits the box around the printed content with a little space to spare.
The crop can apply to every page or only to the pages you list. The tool sets each page's crop box and media box to the new area, so every PDF reader, printer and e-reader shows and prints the trimmed size. The same margins are taken from each page, so pages of different sizes are trimmed to match their own edges.
Limits: cropping hides the content outside the box but doesn't delete it from the file, so the file size barely changes and someone with a PDF editor could restore the hidden part. Never rely on cropping to remove private details; use a redaction tool for that.