the pdf is 40 mb and the form accepts 10

how to compress a pdf on Mac without any app

1. open the pdf in Preview.
2. File → Export.
3. in the Quartz Filter menu, choose Reduce File Size.
4. save under a new name — do not overwrite the original.

for a document that is mostly text with a few images, this usually lands somewhere between a fifth and a tenth of the original and looks fine. free, offline, thirty seconds. if that is your case, you are done.

the same export dialog has three switches next to the filter — Create Linearized PDF, Optimize images for screen, Save images as JPEG. they are worth a look before you conclude the built-in route has no controls at all: it has these, and it has no number.

Apple's own page for the procedure, including those switches: reduce the size of a PDF in Preview

if the pdf came out of a word processor in the first place, the export that produced it is worth getting right — it is where half the weight arrives: convert Word documents to pdf in batches

is there a command to compress a pdf in Terminal?

no, and this is worth stating plainly because the search results are full of Homebrew recipes that quietly assume otherwise. ghostscript, qpdf and pdftk are not part of macOS — on a clean machine all three are «command not found».

sips looks like the answer and is a trap. it lists pdf as a writable format, so the command runs and reports success — but it treats a document as a single image. a 150-page manual of 8.8 mb came back at 115 kb, and the page count went from 150 to one. everything after the cover was gone, and nothing in the output said so.

the python recipes that circulate need PyObjC, which the system python does not have either. so the honest answer to «compress a pdf from the command line on a Mac» is that you install something first.

the same shape of problem shows up on images, where the Finder offers you three words instead of a size — and there the Terminal answer does exist: convert heic to jpg

a custom quartz filter, if you want the dial

there is a real built-in way to change the numbers, and almost nobody mentions it: ColorSync Utility can duplicate the Reduce File Size filter and let you edit its resolution and its jpeg quality. the copy lands in your own filters folder and appears in Preview's export menu alongside Apple's.

it works, it costs nothing, and it is a one-time twenty-minute job with an xml file at the end of it. what it still does not give you is a target: you set a recipe, not a size.

the official route for editing one: modify PDF files with Quartz filters

why the Mac's pdf compression sometimes makes the file bigger

144 dpi and jpeg 0.70: what reduce file size actually does

it is not a compression level. it is a filter with fixed numbers baked in, and you can read them yourself — the file is at /System/Library/Filters/Reduce File Size.qfilter. on macOS 26 they are: resample images to 144 dpi, cap them at 2400 pixels, re-encode as jpeg at quality 0.70.

note those numbers if you have read otherwise. a great deal of the advice online still quotes 512 pixels and 50 %, which were the values before Apple changed the filter — the instructions were right once and are now simply wrong.

the filter is an object with settings rather than a slider, which is why it behaves the same way every time: QuartzFilter

8.8 mb in, 35 mb out: a real case

applied to the DaVinci Resolve manual that ships with the app — 150 pages, 8.8 mb — that filter produced a 35.6 mb file. all 150 pages intact, so nothing failed: the compression ran, and it quadrupled the document.

the reason is inside the file. it holds 354 images that are already jpeg and 189 with an alpha channel. the filter decodes each one, resamples it to 144 dpi, re-encodes it, and flattens the transparency — and for already-compressed artwork that arithmetic runs the wrong way. a document full of large unoptimised photographs shrinks to a third; a document full of small optimised diagrams with soft edges grows.

so «Reduce File Size» is a promise about the operation, not about the result. the only way to know which kind of document you have is to run it and look — which is the loop this page is really about.

why already-compressed images resist a second pass at all is a story about formats, and it explains this one: why your photos are heic

the change to the filter's numbers was noticed independently and is worth citing, because so many pages still describe the old ones: Apple changed Reduce File Size

Preview reduce file size not working?

• the file grew or barely moved — see above; that is the document, not a fault.
• text-only pdfs barely shrink at all. the filter touches images; vector text and line art are left alone, which is why a 40 mb text document has its weight somewhere else entirely.
• a scanned page came back soft. on a scan the whole page is one image, so the text is what gets resampled to 144 dpi. this is the case where people notice too late.
• the document is encrypted. nothing can rewrite it until it is unlocked.

how to compress a pdf on Mac to a size you choose

every route above shares one shape: apply a recipe, save, look at Finder, decide whether to try a different recipe. none of them takes a target. that is the actual cost of the free options — not money and not privacy, since Preview is both free and offline, but the fact that you cannot know the outcome before you commit to it, on a document where the outcome ranges from a third of the original to four times it.

hop's converter shows the resulting size before anything is written, having tested a sample rather than estimated, and the squeeze has a level you set rather than a recipe you pick.

the first and last rows are not courtesies. for one ordinary document Preview is genuinely the right answer, and on privacy the built-in route is exactly as good as ours — the argument about uploading applies to the web compressors in the search results, not to your own Mac.

the module in full — images, video and documents go through the same window: file converter on the features page

when compressing the pdf is not what your Mac needs to do

why is my pdf so large in the first place?

• it is a scan. every page is a photograph, and the size follows the dpi it was scanned at — re-scanning at 200 dpi beats compressing a 600 dpi scan afterwards.
• it has embedded fonts, several of them, in full. common in documents exported from design tools, and nothing image-related will touch that weight.
• it is 300 pages. compression will not fix a page count — split the document and send the part that is wanted.
• it carries form fields, annotations or a signature. compressing can flatten those, and a flattened signature field is a different document legally as well as practically.

• it has to stay readable to a machine. a form headed for an ocr pipeline needs its resolution kept; squeeze it and it fails validation for reasons nobody explains.
• you are emailing it and the limit is the mail server's. a link avoids the whole problem, and no amount of compression turns a 200 mb file into an attachment.

and if the disk rather than the mailbox is the problem, pdfs are rarely where the space actually went: what «system data» is actually using

the number a cleaning app reports for that is worth reading carefully: what the space a cleaner finds is made of

frequently asked questions

why did Preview make my pdf bigger?

Reduce File Size decodes the images inside and re-encodes them at 144 dpi and jpeg quality 0.70. if they were already compressed more efficiently than that — and especially if they have transparency — the result is larger. on the DaVinci Resolve manual it turned 8.8 mb into 35.6 mb.

what does reduce file size actually do?

resamples images to 144 dpi, caps them at 2400 pixels and re-encodes them as jpeg at quality 0.70. the numbers are in /System/Library/Filters/Reduce File Size.qfilter and you can read them yourself. advice quoting 512 pixels and 50 % predates a change Apple made.

how do i compress a pdf in Terminal on a Mac?

you cannot, with what ships. ghostscript and qpdf are not installed, and sips — which does list pdf as writable — collapses the document to its first page: a 150-page manual came back as one page.

can i choose how much a pdf is compressed?

not in Preview, which offers a fixed filter plus three switches. ColorSync Utility can duplicate the filter and let you edit its resolution and quality, which is a real answer and a one-time job with an xml file at the end.

does compressing a pdf reduce text quality?

real text in a pdf is vector and survives untouched. text in a scan is part of an image and degrades with it — which is why scanned documents are the ones that come back looking wrong.

is it safe to use an online pdf compressor?

the file is uploaded to a server you do not control, which for a contract or a passport scan is the whole question. everything on this page runs on your own Mac, including the built-in route.

how do i compress several pdfs at once?

Preview handles one at a time. Automator has an Apply Quartz Filter to PDF Documents action and can be taught the batch; a converter that takes the folder in one drop does it without the teaching.

the tool behind this

done with convert and compress

other things people do

• a folder of heic, and something that wants jpgfile converter
• mov and mp4 are often the same filefile converter
• QuickTime will not open it. the video is fine.file converter