I'm not aware of any mainline CAD package that will import 2D PDF direct to 2D sketches / drawing, or 3D model either. For a while there was 3D PDF as well but it was standalone and did not direct import to any CAD I'm aware of either. If I had PDF of a set of eng dwgs of a prototype locomotive and wanted to build a model, I'd set out reading off dims and scaling them where dimensions are missing, and modeling it from scratch in your CAD of choice . On castings the missing dims / scaling / interpreting the cast details will likely be a major job. You will also have a huge amount of tiny details on production dwgs that you will not need for a model locomotive so the CAD from scratch approach allows filtering that out. (if you COULD somehow load PDF direct, you would probably spend the same amount of time filtering out this detail. One example that comes to mind is oilways and shim / wedges in axle boxes on dwgs of full size engine dwgs, or coring details in full size castings that would not be needed in miniature castings, if used.)

I've been using CAD professionally for over 35 years (yes it's been around that long, and longer) and have used 6 major CAD platforms full time for extended periods. I do try and keep abreast of new products as well. Unfortunately there is no panacea of great CAD for low dollars – and no universal file format readable in all platforms-mostly because CAD companies do not want a universal format – it would reduce their sales.

Have you looked at freecad? Seems to be quite a few guides on youtube. Just save your work often as it can crash unexpectedly.

I use Alibre and just snip the part of the PDF and save as a .jpg. I can then import that image using the "trace" function and the resulting image can be scaled to a known dimension in both z and y as well as rotated if needed and then others taken simply by drawing a line on it and seeing what that line measures. Or more often simply draw the new part over the top of the image

Imported jpg being scaled

First part 3D model drawn and extruded

Drawing main outline to match jpg as closely as possible

Finished 3D Model

I would not want to use it as a way to draw say the frames or other critical parts which are best done using the dimensions on the original and scaled but for getting the profile of odd shaped parts or the outside of castings which are not usually dimensioned it's a useful tool

Jason and Paul – yes many CAD packages can import jpeg for sketching , but the OP asked about direct import of PDF. PDF to jpeg to sketch importing is not the same thing, and accuracy is lost at every step. As others mentioned, PDF images are often distorted in X and Y and not always proportionally. One further point – PDF made from a CAD generated file is likely to be pretty accurate in terms of dims being proportional to features. (yes the dims can be jimmied and overridden, but this is not the case in the majority of PDF I have seen- but be aware). However on manual drafted drawings say anything pre 1978, often when minor size changes were made, for example if a hole changed from 25 to 28 mm, only the drawing dims were edited, the object lines were not erased and redrawn, to save time. Only if a major feature was added or removed or moved the object lines were erased and redrawn. It didn't matter back then because the tradesmen in the shops using the drawings did not scale the drawings, they worked from the dims and transferred the sizes to the workpieces with rules, calipers etc. I know – I did thousands of such "quickie" or "discount drafting" edits under instruction from my supervisors at several firms before they changed to mainline CAD for their engineering. Much better to read the PDF and make CAD from scratch, in my opinion.

MoI will import a PDF vector file directly with all curves remaining editable.

Martin.

Edited By blowlamp on 24/10/2021 14:17:15

Be aware that depending on how the originals were scanned to PDF – and if they'd ever been held on microfilm during their life, there may some lens distortion embedded in the PDF. Lines that should be straight may not be so.

I once tried to scan and convert to CAD some 1970s drawings that had gone via microfilm – it ended up being quicker to manually re-do the drawing from scratch just using the original as a guide and to give dimensions.

You could be lucky, and technically you can use software to correct for lens distortions, but it certainly isn't a 'press the button' process.

Also to extract the meaningful lines, you need a very clean print to start from. There will usually be some speckles and marks to remove manually, which also takes up a lot of time.

Older 'pre-CAD' produced drawings often contain features which are simply not correctly sized – it was always intended that the dimensions would be used to drive manufacture, not the profile on the paper. The paper drawing was good enough to convey the intent, but 'DO NOT SCALE' was on the drawing for good reason.

The problem is PDF not MOI. I don't doubt MOI will read vectors, but they're only useful up to a point. MOI can only work with what's in the PDF, which may be superficial. Put a paper plan into a scanner, select PDF as output. and see how well MOI converts the result. Or not!

A 3D-cad package's file format can produce an SVG and the SVG can happily be converted into gcode. However. information is lost at each stage making it hard to reverse the process. gcode can't be converted back into the original SVG, and SVG can't be converted back into the original CAD format. PDFs are the same: what's extracted from them is more-or-less lacking compared with the original. PDFs lose information compared with a real DXF.

Nothing wrong with PDFs for their intended purpose, but they're not a good way of transferring technical drawings between CAD packages. Hurrah if it works, but don't expect much.

Dave

That's the same method I use with Alibre, he just saved it as a .jpg and used that as a guide.