How to compress many PDFs at once on a Mac, not one by one

Preview compresses one PDF at a time, so a folder of thirty invoices means thirty trips through File > Export. macOS can batch the job with an Automator Quick Action or a Shortcuts action, but both apply one fixed setting to every file and neither can aim at a size. When the files have to land under a number, drop them all into a tool that takes one target size and works through them as a list.

Sort the folder first: not every PDF needs it

A folder called “Invoices 2026” is rarely one kind of file. Some PDFs were exported by accounting software or downloaded from a bank, and those are text: usually 20 to 300 KB each, already about as small as they will get. Others came from an office copier, a phone scanner app or a photo of a paper receipt, and those are pictures of pages, often 1 to 5 MB each. Only the second group is worth compressing, and running the first group through a filter can even make those files slightly bigger.

1. Open the folder in Finder and choose View > as List (Command-2).
2. Click the Size column header so the largest files sit at the top.
3. Select everything over about 1 MB and drag it into a new folder called “To shrink”. Leave the small ones alone.
4. Open one of the big files in Preview and zoom well in on a line of type. Letters that stay crisp are text; letters that turn fuzzy or blocky are a picture of the page, which means a scan.

Note the page counts too. A one-page receipt and a fourteen-page signed contract should not get the same size target, which matters in a moment.

Preview handles one file at a time

Preview’s Reduce File Size filter lives in File > Export, under Quartz Filter, and it acts on the document in front. That is fine for one attachment. For thirty, it means thirty exports, thirty new names and thirty chances to save over an original by accident.

The filter is also one fixed recipe. On macOS Sequoia, its settings file asks for every image at 144 pixels per inch with JPEG compression, whatever the page holds. The full Preview walkthrough, including a gentler custom filter built in ColorSync Utility, is in how to compress a PDF on a Mac, and if the result came out soft, Reduce File Size in Preview made the PDF blurry explains what to do instead.

Automator and Shortcuts can batch it, bluntly

Both built-in automation apps can run a filter over a whole selection.

Automator

1. Open Automator from Applications and choose Quick Action.
2. At the top, set the workflow to receive PDF files in Finder.
3. Search the actions for Apply Quartz Filter to PDF Documents and drag it into the workflow. Automator warns that this action changes the PDF files passed into it and offers to add a Copy Finder Items action so the copies are changed instead. Click Add and point Copy Finder Items at a new folder; without that step, the action rewrites your originals and there is no undo.
4. Pick Reduce File Size in the filter list. Custom filters you made in ColorSync Utility are generally listed there too.
5. Save it with a name such as “Shrink PDFs”. In Finder, select the files, right-click, and choose it under Quick Actions.

Automator also has a Compress Images in PDF Documents action. Its only options are a compression type and a quality setting, with no control over resolution, so it does far less for a heavy scan than a filter that downsamples.

Shortcuts

Shortcuts has an Optimize File Size of PDF action. Apple’s own description says it compresses the images in the PDF, and that if they are already compressed it might not have a measurable effect. Put it in a shortcut that runs as a Quick Action in Finder, followed by a Save File action pointed at an output folder (the wording varies by macOS version). Expect some fiddling, because the action’s default output name is “Optimized PDF”, not your invoice’s name.

The shared weakness is the one that matters here. Every file gets the same treatment, whether it is a crisp text invoice or a muddy color scan, and nothing checks the result against a limit. If the portal takes 2 MB per file and six of thirty come out at 2.4 MB, you find out one upload at a time.

One target size for the whole folder

Manatee turns the question around. Its Shrink mode takes a size in MB and finds the quality that fits, and its window keeps a job list, so a folder goes through in one pass.

1. Open Manatee, choose Shrink, and type the target size in MB.
2. Select the PDFs in Finder and drag them onto the window. Dropping them on the menu bar icon works too, as does right-clicking and choosing Services > Fix with Manatee.
3. Each file appears as its own row in the job list, with its own progress.
4. Every result is written as a new file next to its original. The originals are never modified, so a target that turns out too tight costs nothing but a second run.

The target applies to each file, so group the files before you start: run the long contracts at one number and the one-page scans at another. If the limit is a total, such as 10 MB for everything attached to a claim, and the portal accepts a single PDF, merge the scans first (the questions below show how in Preview) and give the merged file the whole budget, say 9 MB. Thirty separate files sharing 10 MB works out to about a third of a megabyte each, which is a job for the Automator route above, followed by a check of the total.

It runs entirely on the Mac, with no upload and no account, which suits a folder full of bank details, addresses and tax numbers. Every feature is free for the first 24 hours, then $9 once.

Give it the scans you sorted out at the start, not the text PDFs, which have little to give. Manatee does not merge, split, delete pages or make a scan searchable. The same queue idea works for video, covered in how to batch compress videos on a Mac.

What size is realistic for scans and text PDFs

Rough figures for letter-size pages, worth knowing before you type a target:

• Text PDFs (exported invoices, downloaded statements): 20 to 300 KB for a few pages. Leave them as they are.
• A one-page scan of printed text, in gray or black and white: about 150 to 500 KB at a comfortable reading quality.
• A one-page scan with color (a logo, a stamp, a highlighter mark): roughly double or triple that, so 0.5 to 1 MB.
• A phone photo of a receipt saved as a PDF: often 2 to 4 MB as captured, and usually fine at a few hundred KB.

A workable budget is about 300 KB per page for gray scans and twice that for color. Thirty single-page scans therefore come to about 9 to 10 MB together, which is why a 10 MB total limit is tight but reachable, while a 5 MB one, about 170 KB a page, leaves almost no room before fine print goes soft. Below about 100 to 150 KB a page, small type such as invoice numbers, tax IDs and line totals starts to blur. If the paper is still on your desk and the scans were made at 600 dpi in color, rescanning at 200 dpi in gray beats any compression.

Before you send the batch, open three or four of the results at random, choose View > Actual Size, and read the smallest number on each page. If anyone will need to search or copy text from the files, try selecting a line in one of them too.

Questions

Why did some files barely shrink, or get bigger?

They were mostly text, or their images were already compressed. These tools only work on images, and re-encoding an efficient image can add bytes. Keep the original of any file that did not improve.

The portal wants a single PDF, not thirty. What now?

If they are all scans, merge them and shrink the merged file to the portal’s limit in one go. If the set mixes text PDFs with scans, shrink the scans first and merge afterward, so the text pages are left as they were. To merge in Preview, work on a copy: select the first PDF in Finder, press Command-D, and open the duplicate. Choose View > Thumbnails, drag the other files from Finder into the sidebar, put the pages in order, and choose File > Export as PDF to save the result under a new name.

My bank statements are password-protected. Will they compress?

Not while they are locked. Open each one in Preview with its password, export an unlocked copy, and compress the copies. No compression tool, Manatee included, gets around a password you do not have.