How to Attach a PDF or DWF File as an Underlay in AutoCAD

By Bill Fane

You can attach a PDF or DWF as an underlay in AutoCAD. The Adobe PDF (Portable Document Format) format has been around for a very long time, and for a while it seemed like Autodesk was trying to supplant it with its own universal file format: DWF (Design web Format). That didn’t happen, but if you can’t beat ‘em… . AutoCAD includes a very acceptable PDF printer driver, and both PDF and DWF are suitable candidates for external reference attachments.

You could think of a DWF as DWG Lite because it looks just like a drawing file and contains some of the actual drawing file data.

You create both DWFs and PDFs from within AutoCAD in one of two ways. Either choose Plot and then select a DWF or PDF option in the Printer/Plotter name list, or choose Print→Batch Plot from the Application menu and then choose DWF, DWFx, or PDF from the Publish To area of the Publish dialog box.

Both file types are compact and secure. Because you can’t edit either PDFs or DWFs in AutoCAD, both formats are ideal for two purposes:

  • You can post DWFs or PDFs on the web.
  • You can send your drawings to consultants and clients in a form that they can’t mess up.

Oops, AutoCAD 2017 changed part of the foregoing a bit. It is now possible to edit a PDF file in AutoCAD, but there are quite a few limitations.

You can attach PDFs or DWFs to your drawing files in pretty much the same way you attach drawings as external references. DWFs and PDFs attached to drawing files are referred to as DWF underlays or PDF underlays.

As with DWF and DGN attachments, you can object-snap to entities in the PDF underlay by enabling the Snap to Underlays function in the Reference panel slideout on the Insert tab. Setting PDF parameters is virtually identical to setting DWF parameters, and you can attach a PDF to your drawing by using exactly the same steps as the ones that follow.

Follow these steps to attach a DWF or PDF file as an underlay:

  1. If the External References palette isn’t already open, click its icon on the Palettes panel of the View tab to open it. Use the toolbar at the top of the palette to attach an external file as an xref, a raster image file, or a DGN or DWF underlay. See the online help for information on attaching DGN files.
  2. Click Attach DWF or Attach PDF and then locate the file you want to attach. The Select Reference File dialog box appears.
  3. Browse to find the file you want to attach, select it, and then click Open. The Attach DWF Underlay or the Attach PDF Underlay dialog box appears.
  4. Specify the parameters for the DWF or the PDF in the dialog box. Parameters include specifying a sheet, the insertion point, scaling factors, rotation angle, and path type. You can set these parameters in the dialog box or specify them onscreen, just like you can do when inserting a block, attaching an xref, or attaching an image.
  5. Click OK. The externally referenced DWF or PDF file appears in your drawing.
Attach PDF Underlay dialog box
The Attach PDF Underlay dialog box.

Neither PDF nor DWF files are as precise as DWGs, and that’s why their file size is a lot smaller. When using object snaps to locate points in DWFs, you may see the word approximate on the Object Snap tooltip. If this is a problem, you can increase the precision of your DWF file when you create it.

AutoCAD allows you to import about 20 different file formats into an AutoCAD drawing. Most of these are 3D modeling formats. They are imported into model space (not attached or xref-ed), and are used as the basis for additional 3D modeling and editing and for generating 2D working drawings from them.