@forasposeissues Please note that Docx->Pdf conversion is a very resource-intensive operation during which Docx float-format is split into pages, the layout is adjusted to that of MS Word, and the non-text content is rendered. Thus, conversion time directly depends on the document size and the number of images, as well as on computer performance. For their part Aspose.Words are constantly working to improve efficiency and processing algorithms.
The conversion time for “Big doc with images.docx” by your code makes 7 seconds on my computer at the moment. If on your part conversion takes more or less equal time, then, unfortunately, we could only recommend a more powerful computer, since there are currently no settings in Aspose.Words that allow a significant increase in speed.