How to Compress a PDF to 500 KB, 2 MB, 5 MB or 10 MB on Mac

Use the number the form gives you. File Acture aims at what you type and keeps the highest image quality that fits, so a larger limit means a sharper file, and typing less than you need only costs quality.

• The form names one limit: type it as it is. When File Acture can reach the number, the result is at or under it, so you needn’t subtract a margin.
• One limit per file: every file in a run gets the same target, so group your files by limit and run each group.
• One limit for the whole application: divide it by the number of files and type that.
• No number given: File Acture starts at 5 MB. Try that first and go lower only if the form turns the file down.

Not to a set size. Preview’s Reduce File Size filter, in the Quartz Filter menu when you export a PDF, is one fixed recipe: a large scan can stay above your limit while a small file comes out blurry. See what the filter really does.

It is fine when “a bit smaller” is all you need, but it cannot aim for 500 KB or 2 MB.

Open Compress PDF, set Compress by to Target size and enter the limit. Type any number and choose KB or MB, or pick 1, 2, 5, 10 or 25 MB from Presets. 500 KB isn’t a preset, so type 500 and choose KB; 0.5 MB works too.

File Acture counts in decimal units, like Finder: 1 MB is 1,000,000 bytes and 500 KB is 500,000 bytes. A file under 2 MB therefore also passes a site that counts a megabyte as 1,048,576 bytes.

We ran four PDFs from our test collection through each target, and the table below shows the results. “Smallest possible” means the number could not be reached: File Acture saved the smallest result it could make and added a note.

• 500 KB: realistic for a short document, not for a long one. The one-page scan fell to 291 KB, but the 48-page slide deck stopped at 1.72 MB and the photo report at 3.55 MB, with their images at the lowest quality File Acture uses.
• 2 MB: reached by the slide deck (1.98 MB), with its images at 72 DPI, screen resolution. The photo report still stopped at 3.55 MB.
• 5 MB: reached by both large documents, with the deck’s images at 300 DPI and the report’s at 100 DPI.
• 10 MB: the report reached 9.88 MB with its images at 300 DPI, and the deck’s best quality already fit at 5.96 MB.

File Acture saves the smallest result it can make and adds a note that the number wasn’t reached. If even that wouldn’t be smaller than your original, it tells you the smallest size it can reach and saves nothing. Then you decide what to change:

• Send fewer pages. Extract the pages the form actually asks for, then compress those.
• Split the file. If the form accepts several files, split the PDF into parts and give each part its own target.
• Try grayscale. Convert images to grayscale helps with colored scans of documents that don’t need color. On our photo-heavy test files it saved little: the report’s smallest result went from 3.55 MB to 3.47 MB.
• Check what’s inside. Text, fonts and vector graphics aren’t re-encoded, and neither are black-and-white scans stored as JBIG2 or CCITT, or CMYK, JPEG 2000, indexed and 16-bit images. A 144-page book scan made of JBIG2 and JPEG 2000 images stayed at 6.79 MB at every size, and a 142-page text-heavy guide stayed at 3.09 MB.

Online compressors upload your PDF, which is a real risk for contracts, payslips and ID scans. File Acture compresses on your Mac and never uploads the file.

The free version includes 3 runs on each Mac, with up to 5 PDFs per run, and Pro removes the limits; see pricing. If the file is going into an email, see what actually fits in a mailbox.