What Is an ASPX File?

This article explains what ASPX files are and how they're used, what to do if you download one by mistake, and how to convert one to a more usable format.

What Is An ASPX File?

A file with the ASPX file extension is an Active Server Page Extended file that's designed for Microsoft's ASP.NET framework. It's also called a .NET web form. Although they look fairly similar, ASPX files aren't the same as Web Handler files that end in ASHX.

A web server generates these files, and they and contain scripts and source codes that help communicate to a browser how a web page should be opened and displayed.

More often than not, you'll probably only see this extension in a URL or when your browser accidentally sends you an ASPX file instead of the one you thought you were downloading.

How to Open Downloaded ASPX Files

If you've downloaded an ASPX file and expected it to contain information (like a document or other saved data), it's likely that something is wrong with the website, and instead of generating usable information, it provided this server-side file instead.

In that case, one trick is to simply rename it to whatever you expect it to be. For example, if you expected a PDF version of a bill from your online bank account, but instead got a file with this file extension, rename it to bill.pdf and then open that. If you expected an image, try renaming it to image.jpg. You get the idea.

The issue here is that sometimes the server (the website you're getting the file from) doesn't properly name the generated file (the PDF, the image, the music file, etc.) and present it for downloading as it should. You're just manually taking that last step.

Sometimes the cause of this problem is browser or plug-in related, so you might have luck loading the page that's generating the ASPX file from a different browser than the one you're using now. For example, if you're using Edge, try switching to Chrome or Firefox.

How to Open Other ASPX Files

Seeing a URL with ASPX at the end, like this one from Microsoft, means page is being run in the ASP.NET framework:

https://www.microsoft.com/web/downloads/platform.aspx

There's no need to do anything to open this type of file because your browser does it for you.

When the browser displays the page, it looks completely normal; this is what the source code behind the page looks like in that example:

The actual code in the file is processed by the web server and can be coded in any program that codes in ASP.NET. Microsoft's Visual Studio is one free program you can use to open and edit these files. Another tool, although not free, is the popular Adobe Dreamweaver. Sometimes, an ASPX file can be viewed, and its contents edited, with one of these free text file editors.

How to Convert an ASPX File

ASPX files have an explicit purpose. Unlike images, like PNGs or JPGs, where a file conversion retains compatibility with most image editors and viewers, ASPX files will stop doing what they're meant to do if you convert them to other file formats.

Converting one to HTML, for example, will certainly make the HTML result look like the ASPX web page. However, since the elements of the ASPX file are processed on a server, you can't use them properly if they exist as HTML, PDF, JPG, or any other file you convert them to.

However, given that there are programs that use ASPX files, you can save one as something else if you open it in an appropriate editor. Visual Studio, for example, can save one to HTM, HTML, ASP, WSF, VBS, ASMX, MSGX, SVC, SRF, JS, etc.

Still Can't Open It?

Be careful to avoid confusing other similarly named file extensions for one that ends with .ASPX.

For example, ASX files look like they might be related to ASPX files, but they could actually be Alpha Five Library Temporary Index files that only work within the context of the Alpha Anywhere platform. The same is true for others like ASCX.