swolber, 

I'll add to what N.S. said, software is not the main thing. Software is just a tool. I mentioned below, three desktop publishing software. They are decent software. However, the software you use is not what will make a good portfolio. There is nothing that replaces skill. 

The software is the least of your problems. It is just a tool but they are not magic boxes that will guarantee that your portfolio will be better than someone else's portfolio. You need to learn the software but you'll more importantly need to develop the skills in composition and communication of your design thinking and development process. The portfolio reviewers aren't going to give even one shit about the software you used. 

Therefore, I think you'll want to take the time to get advice on producing content and assembling the portfolio content. Take the opportunity to get that advice from people. Don't dwell on what software tool is best. For what are doing, it really doesn't matter.

Desktop Publishing software. MS Word (part of Office suite) is good for textual reports but not so ideal for portfolio which typically is going to use more fancier desktop publishing features. 

 Therefore, you should use Adobe Indesign or Affinity Publisher or Scribus because they have the ability to do more advanced page layout and features. Content and good layout matters. 

I would recommend one of the three Desktop publishing software (note: Desktop Publishing is not word processor even if you end up with a document. These programs will export to PDF which is standard. They want it in PDF format so they don't have to have the specific software to look at it in its 'proprietary' format.

Others can provide you with better advice on portfolio creation but the software I mentioned are three common software that has commonly been used for making a portfolio. 

The first two cost money. The last one is free, the last I recall, and is a good option for open source free desktop publishing software. Affinity Publisher is a fairly nice and relatively low cost alternative to InDesign and is fairly similar in how it looks and its functionality yet costs considerably less... and it can be worth the money if you use it for more than just this portfolio work.

The three I mentioned are adequate for anyone to make a good portfolio. If you don't know how to make a good portfolio using the said software is because either you don't know how to use the software or you lack knowledge and skill regarding creating a good portfolio. It's not all about the software or software skill. It helps but it doesn't stop there.