A PDF can contain several page boundaries serving different purposes. The visible page in one viewer may therefore be different from the finished trim boundary expected by a print supplier. Inspect the actual page boxes before resizing the artwork or changing print scaling. A discrepancy in boundaries is not automatically a discrepancy in the picture's pixel resolution.
Name the boundary that matters
Ask which dimension the recipient requires: the complete sheet, the displayed crop, the finished trim or the bleed allowance. Record that answer beside the supplied template. “The PDF must be 100 millimeters wide” is ambiguous if nobody identifies the intended box.
Adobe's crop-page documentation identifies CropBox, ArtBox, TrimBox and BleedBox controls and notes that cropping hides content rather than removing it. These are PDF-editing concepts and Acrobat controls. A screenshot of a cropped preview cannot establish that all relevant PDF boundaries were updated correctly.
Compare numbers before changing the drawing
Keep the original PDF and inspect a copy with a capable external PDF application. Record the box dimensions and their offsets, not just a viewer's one-line page-size label. Check whether the trim is centered within the expected bleed. Include more than the first page when the document has mixed formats.
Compare those values with the supplier's instructions. If the artwork is correctly positioned but the wrong boundary is being reported, correct the source layout or the appropriate box settings. Scaling the whole page until one label matches can change typography, margins and the intended physical size of a portrait.
A hypothetical four-box check
Suppose a proposed card has a finished trim of 100 by 150 millimeters and an agreed 3-millimeter bleed on each side. Its expected bleed extent would be 106 by 156 millimeters, subject to the supplier's template. A reviewer seeing 106 by 156 in a viewer should first identify which boundary that label represents, rather than declaring the finished card too large.
This is a planning example, not a validated production PDF. Create a review table containing page number, box name, width, height and expected value. Keep any crop marks outside the finished design according to the actual print workflow. Do not turn the example's bleed into a universal recommendation.
Reopen the exact delivery copy
Accept when the recipient's required box has the approved dimensions, artwork remains positioned correctly and all relevant pages agree with the template. Reject a correction that fixes one label while cutting off bleed or moving the intended trim across a face. Inspect a physical proof when the item requires manufacturing approval.
Save the source layout and the checked PDF separately. Imagild's Skills can develop the visual artwork; a generated image has no automatic authority over downstream PDF page boxes. Delivery dimensions belong to the external layout and print handoff, and should be recorded in a way the supplier can verify without guessing from a preview.