BASALT · JOURNAL
Reordering, rotating, and deleting PDF pages on a Mac
A scan comes back with page 7 before page 6, half the pages sideways, and a blank sheet where the feeder double-fed. Fixing that on a Mac takes a minute. Doing it so the result survives the next person opening the file means knowing what these operations touch.
What these operations change
Reordering does not move page content. The pages live in a page tree, a root /Pages node whose /Kids array points at further nodes and at /Page objects. Reordering rewrites that array, leaving content streams, fonts, and images untouched, which is why it is lossless and fast on a 900-page file.
Deletion removes entries from the same array. Whether the objects leave the file is separate: they become unreferenced, and only a writer that rebuilds the document drops them. A deleted page still in the bytes is recoverable, which is why deletion is not a substitute for redaction.
Rotation is the one people get wrong. A page carries a /Rotate entry, a multiple of 90, telling a viewer how to turn the page when displaying it. The content coordinates do not change. Preview sets this value, correctly and permanently once exported, but anything reading content coordinates without honoring /Rotate still sees the original orientation.
What Preview handles well
Preview's thumbnail sidebar is a competent page organizer and pretending otherwise would be silly. View then Thumbnails, drag to reorder, select and press delete, command-R or command-L to rotate. Drag another PDF in to insert its pages, drag a thumbnail out to the Finder to extract it, then File then Export as PDF.
Three limits are worth knowing.
It does not preserve document structure through heavy editing. Bookmarks pointing at pages you moved or deleted are the first casualty, and form fields on inserted pages often stop working, since the AcroForm dictionary is document-level and page editing does not reconcile it.
It saves by appending. Rather than rewriting the file, Preview typically adds changed objects at the end with a new cross-reference section, the incremental update mechanism the format defines. Deleted pages are unreferenced but still present.
It has no bulk operations. Rotating every fourth page is a manual click-through, and moving forty pages to the front is one long drag through a scrolling sidebar, the operation most likely to end up off by one.
Why sideways scans persist after rotating
Two things can be sideways: the displayed page, controlled by /Rotate, and the image inside the page, drawn by the content stream's transformation matrix.
A scanner that fed a sheet in landscape usually produces a landscape MediaBox with an image filling it, and /Rotate 90 displays it upright. A scanner that wrote a portrait MediaBox containing a rotated image still looks wrong, because you rotated the page rather than the content. Tell them apart by aspect ratio: if the page displays tall but the writing runs across the short edge, the content is rotated inside a page of the wrong shape, and the fix is re-scanning or a tool that transforms the content stream.
/Rotate also affects where a stamp lands. Rotate pages and then apply Bates numbering, and the stamping tool has to apply the inverse rotation or the numbers appear sideways in the wrong corner.
Inserting blanks, files, and pages from another tab
Three insertions cover almost every case. A blank page, to force a duplex-printed document onto correct sides or to hold a placeholder for an exhibit. It needs a MediaBox matching its neighbors, not a hardcoded letter size, or the printed result steps in and out.
Pages from another PDF at a chosen position, which is what Preview's drag-into-sidebar does, with the caveats above.
Pages moved between two open documents. This comes up constantly during assembly and no built-in Mac tool does it well, since it needs both files present at once with a target position in each.
Verifying before you send
Check the page count. If you deleted four and inserted one, it should have moved by three, which catches the drag that dropped a page somewhere unintended. Check orientation on every page, not only the ones you rotated.
Then check the outline and any form fields. Click a few bookmarks to confirm they land where they claim, and type into a field. Both take thirty seconds and catch failures invisible in a page-level review. If the file is going to a third party, its non-visible content is worth a look too, since page editing does not touch metadata, as in removing PDF metadata on a Mac.
Frequently asked questions
How do I reorder pages in a PDF on a Mac?
Open the PDF in Preview, choose View then Thumbnails, drag the thumbnails into the order you want, then choose File then Export as PDF. Reordering only rewrites the page tree, so no content is re-encoded and nothing loses quality. On long documents a grid view with multi-select is less error-prone than a scrolling sidebar.
How do I permanently rotate a PDF page on a Mac?
Select the page in Preview's thumbnail sidebar, press command-R or command-L, then choose File then Export as PDF so the rotation is written into the new file. This sets the page's /Rotate value, which every conforming viewer honors, making it permanent rather than a display setting. If the page still looks wrong, the image is rotated inside the page.
Why does my PDF still look sideways after rotating?
Because the rotation is inside the page content rather than on the page. Setting /Rotate turns the whole page when displayed, but if the scanner wrote a portrait page containing a sideways image, turning the page makes the shape wrong too. Check whether the page's proportions match what you see.
Does deleting a page from a PDF actually remove the data?
Not necessarily. Deleting removes the page from the page tree, but its objects can remain as unreferenced data, especially when the save is an incremental update that appends changes rather than rebuilding the document. To be certain the content is gone, use a tool that writes a clean new file, and for sensitive text use redaction.
Can I add a blank page to a PDF on a Mac?
Preview has no insert-blank-page command, so the usual workaround is making a one-page blank PDF and dragging it into the thumbnail sidebar at the right position. An application with an insert-blank action gets the geometry right, since the blank must match its neighbors' MediaBox. This matters most for duplex printing, where a missing blank shifts every later sheet.
Will reordering pages break my bookmarks?
It can. Bookmarks hold destinations that resolve to specific pages, so an editor that rewrites the page tree without updating the outline leaves entries pointing at whatever now sits in that position. Preview's page editing does not carry outlines through reliably, so check the bookmark sidebar after a reorder.
How do I move pages from one PDF to another?
Open both documents in Preview with thumbnail sidebars showing, drag pages from one sidebar into the other, then export both files. This works, though juggling two windows makes it easy to drop a page in the wrong place. An application where documents open as tabs and pages can be sent to another open file is more reliable.
Is there a page limit for reordering large PDFs?
No meaningful one in the format, since the page tree is a balanced structure precisely so viewers can find page N without walking every node. The practical constraint is the interface: a scrolling thumbnail sidebar becomes unusable long before the file does. For several hundred pages, prefer range-based operations.
Doing it in Basalt
Basalt's organize tool reorders, rotates, and deletes pages, inserts a blank page or pages from another PDF, and moves pages to another open document, writing every change to a new file so the original is never modified. Documents open as tabs in one window, which is what makes moving pages between files practical. The engine runs in a sealed process with no network entitlement, enforced by macOS at the code-signature level, so nothing is uploaded and there is no telemetry. Organizing is one of 18 tools in the same window, next to merge and split. It is $29 once for up to three Macs, with a 24 hour free trial, at basaltformac.com.
Redaction that proves itself
Basalt destroys the content you mark, then re-opens the file it wrote and proves the content is gone before it saves anything. Your documents never leave your Mac.