How to Reduce PDF Size of CAD Drawings for Email and Submittals

Two different things make a CAD PDF big: images, and an enormous number of vector objects. They need different fixes, and only the first is something a PDF compressor can do much about.

Images are the easier case. Autodesk’s Revit export help says that when high-DPI raster images are used on a sheet, “the size of the exported PDF will be large,” and it names 300 DPI or lower as the best practice (Autodesk Revit help, read 11 October 2026). Archicad has the same control in its PDF options: a limit on image resolution, with images already below the limit left as they are, and a “Compress all images” option that saves them as JPG at 80% (Graphisoft Archicad help, read 11 October 2026). If you can still open the source model, fixing the image resolution there is the cleanest route.

The second case is a dense plot: topography, point clouds drawn as thousands of small objects, hatches, stacked xrefs. That is vector data, and a PDF compressor that resamples images has nothing to resample. We cover the evidence below. Before you pick a tool, work out which you have.

How do I tell vector from raster in a PDF?

• Open the sheet in Preview and zoom to 800% on a line. Crisp edges at any zoom mean vector. A staircase of pixels means a raster image.
• Select the text with the cursor. If you can highlight words, it is live text. If the cursor draws a rectangle over the page, the page is a picture, as with a scan.
• Compare file size to page count. A few megabytes per page for a drawing that looks like simple lines can point to embedded images.

Not in any way that changes the size much. Smol’s PDF presets cap the pixel size of embedded images and re-encode them. Vector linework, text and fonts are not raster data, so they are left alone.

We measured it. An 8-page file with only text and vector artwork went from 7,095 to 7,077 bytes at every preset, a 0.3% saving (Smol 1.0.34; method in what PDF compression presets actually do). That is one test file, but it shows the ceiling for a sheet that is only vector artwork and text: expect close to nothing.

Scanned and image-heavy sheets behave very differently, because the page is an image. In our scanned PDF test, a 3-page 300 PPI color scan was cut from 5,017,560 to 288,609 bytes, 94.2% smaller. That result came from a chain: a separate free tool, OCRmyPDF, added a text layer first, and Smol’s Medium preset ran second. Smol itself does not OCR. It is one test file, so use it as a direction, not a promise.

There is no single limit. The cap belongs to whichever inbox or project portal receives the file, and your spec section or the portal’s own help page states it. The email limits below are the ones we could confirm.

Plan for email encoding. It adds about 37%, so the working target for a 25 MB cap is 18 MB and for an unknown recipient it is about 7 MB, as worked out in getting a PDF under Gmail’s limit. Smol sets image size and quality, not output bytes, so it cannot promise a file will land under a cap. Run it, read the size, and step to a lower preset if the file is still over. If a submittal package is split across several PDFs, a portal may check each file or the total, so find out which.

Pick by sheet type and the print size you need to read. Presets cap the longest edge of each embedded image in pixels, not in DPI, so the sharpness you get depends on how large the sheet is.

The PPI columns are our arithmetic: pixel cap divided by the sheet’s long edge in inches. A 600-pixel cap on a 36-inch sheet is under 20 PPI, which cannot hold a dimension string, so Tiny is the wrong choice for drawings. Even Original is not lossless: it re-encodes and resamples anything above 2,400 pixels. Quality for the presets runs from roughly 25 (Tiny) to 88 (Original). Those are fixed by the preset, not something you type. No PDF preset strips metadata; use Smol’s separate strip-metadata operation for that, and read how to remove metadata from a PDF for what that does and does not clear.

For a scan that must stay legible when plotted, Large is where we would start, and we would check a title block and the smallest dimension text at 400% before sending. Those are starting points, not measured thresholds. For how presets work in general, see the presets explained. Presets live in the app on one Mac, so a team that wants matching output should write the settings down and recreate them on each machine.

Do the package in one pass, then sort by size. Mixed files can go in together.

1. 1

   Export from CAD at a sensible image resolution first

   If you have the model, set the image limit in the export dialog (300 DPI or lower, per Autodesk). Smol is for the files you cannot re-export.

2. 2

   Drag the folder of PDFs into Smol

   Whole folders are fine, and you can include photos or product-data images in the same drop. Batch details are in batch compressing PDFs.

3. 3

   Choose a preset by sheet type

   Large for scanned drawings you will zoom into, Medium for scanned reports, Small only for cover letters. Pure vector sheets can stay out of the batch.

4. 4

   Run it and read the per-file savings

   Smol shows the size before and after for each file. A vector sheet that saved almost nothing is expected, and if compressing would make a file larger, Smol keeps the original.

5. 5

   Open the worst sheet and zoom in

   Check the title block, the smallest dimension text and a hatch at 400%. If anything is soft, step up one preset and run that file again.

6. 6

   Check the package against the cap and send

   Sort by size, compare to the limit with 37% of encoding in mind for email, and upload the _compressed copies.

For a comparison with Adobe’s tool, see the Acrobat alternatives for Mac and the best PDF compressor for Mac. Smol never uploads a file, which helps when a client contract limits where project documents can go. Related reading: the architects drawings PDF guide and construction contractor files.

• The PDF is pure vector from CAD. We measured 0.3%. Reduce objects, xrefs and image resolution at plot time instead.
• You need to edit, merge, split, sign or redact. Smol does none of these. It also does not OCR, so a scan stays unsearchable until another tool adds text.
• You need a file exactly at a byte limit. Smol sets image size and quality, not output bytes, so you check and rerun.
• You need to open or convert DWG, DXF or native model files. Smol handles the PDF, not the CAD format.

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