AutoCAD Tip – Slow opening, crashing PDF files generated by AutoCAD?

by Dennis Collin

I recently had a conversation with a customer using AutoCAD for the creation of event planning drawings. The drawing was quite large and was slow to open. When producing output PDF files, the files opened slowly and ultimately caused the Adobe Acrobat reader application to ‘lock up or crash’ when attempting to view or navigate the document.

This was causing a massive problem with the customer, delaying the coordination and setup of the events they needed to organise at the venue. I was tasked with finding out what was causing the problem with the slow performing PDF output.

Drawings related to facilities management and event planning are frequently beset by problems and issues with data being obtained from old files or 3^rd party CAD systems.

Many of these issues can be reduced using AutoCAD’s file maintenance commands such as Purge, Audit and Overkill, to refine the number of elements, redundant layers, and styles. The key problem of the file, however, was that many text elements were using AutoCAD legacy SHX fonts which are not supported in the PDF format.

Fig 1. Large number of text comments within a PDF can cause severe performance issues.

True type fonts are supported and work as expected, but when there are a great number (thousands) of SHX text elements within a file,  it causes a problem in that these legacy elements get stored as ‘comments’ within the PDF document. These elements can be identified within Acrobat reader as AutoCAD SHX text, and it is these sheer number comments causing the PDF reader to open the document slowly and eventually crash.

Performing either of the following tasks will cure the problem:

• Change all the text styles referencing SHX fonts in the drawing to True Type Font Equivalents ie. Use Simplex.TTF rather than Simplex.SHX

OR

• Set the PDFSHX system variable to Zero (0) , turning it off. This will ensure that no additional comments are created when exporting a PDF file. Text that uses SHX fonts will be preserved visually as geometric objects and will still display and print as expected. The default value is 1 (On) which creates comments from text objects using SHX fonts.

From AutoCAD 2024/LT 2024 onwards there is a superstate setting (2) for the PDFSHX variable that will not only ensure the SHX text will display and print but also the text string will be searchable within the PDF reader.

However, for best PDF performance when working with files containing many text elements using the SHX font I would recommend setting the PDFSHX system variable setting at Zero.

The setting is stored within the system registry and will solve the PDF performance problem for all future generated PDF documents generated from that build of AutoCAD or AutoCAD LT.