The TrimBox. When the profile has a trim size, the TrimBox is set to that size, centred on the MediaBox and kept inside it. On a page rotated by 90 or 270 degrees, width and height swap so the finished piece still matches. A TrimBox that already has the right size, within the profile's tolerance, is kept wherever it sits. When the profile accepts any size and a page has an ArtBox but no TrimBox, the ArtBox is promoted to the TrimBox.
The BleedBox. The BleedBox is set to the TrimBox expanded by the profile's minimum bleed on every side, then kept within the MediaBox. An existing BleedBox that already contains that area is left alone. With the starting profile, a Letter trim of 612 × 792 pt on a 630 × 810 pt page gets a BleedBox that fills the page.
The Rotate value. PDF stores page rotation as a multiple of 90 degrees. Values outside 0, 90, 180, and 270, such as 450 or -90, are rewritten to their plain equivalent, so every program reads the page the same way. Content streams are never rewritten.
Everything else stays. Only those entries change. The artwork, images, colour, fonts, and transparency in the fixed copy are the customer's own, so a fixed copy never introduces a new colour space or flattens anything.
Where it is saved. Save fixed copy opens the Windows Save As dialog with the customer's file name plus -fixed.pdf, for example spring-flyer-fixed.pdf. Choosing the original file as the target is refused, so the copy can never replace the file the customer sent.
What you see afterwards. The Fixed copy saved confirmation names the new file, gives its SHA-256, and lists each change, for example "Page 1: TrimBox absent → [9 9 621 801]", and ends with "The original was not changed." When nothing needs correcting, the app says Nothing to fix and writes no file.
Signed files. When the original carries a digital signature, the confirmation says so: any change to a signed PDF means the copy's signature no longer validates, which is useful to know before sending it on.
Check the copy. Open the fixed copy with Open another PDF and check it against the same profile. The trim-box and bleed findings clear, the preview draws the new Trim and Bleed boxes, and you can save a fresh report for the job folder.