Two things that can cause a poor quality result are (a) use of too low a bitrate, or (b) rendering to a much smaller frame size than the size of the project. If the text looks sharp in the video preview, but not in the rendered file, one of these factors might be the cause.

Make sure you are judging the quality at BEST resolution in Preview. Otherwise, without us seeing the quality of the scan, we cannot offer much advice.

Edit: the screen grabs below were uploaded using the forum uploader. When I try to view them in the context of my comment they appear on my screen so small as to be worthless. I haven't added screen grabs to a comment before so if someone could advise me how to do it in a way that produces an image that is readable, I'd appreciate that. What follows below is my original comment.

Thanks for the comments. Other things intervened and I had to put this project aside, but now I'm back to finish it and am still looking for help.

The goal is to create a DVD of two complete performances of a community theater production of a musical. I will be putting this on a dual-sided DVD that will contain about 4 hours of video, so my final bitrate will be about 4000. Since the video during the overture is just black, I want to include a video of the program for the musical, presented one page at a time and with the page turning effect. I got the program pages as pdf files, two pages per file and high resolution. I used Gimp to separate the pages so there is only one per file and also to convert the file to png, since I have never been able to make Vegas import a pdf file. The resulting png file is about 4000x5000, with some variation since I split the pages manually.

I created the page turning effect in a separate project and rendered that as an uncompressed avi. Here are the project settings for this page turn effect veg:

And here is a screen grab of one of the program pages as it appears in the avi file I rendered from the page turn veg (as played on my computer screen by VNC):

I then put this avi on the timeline for the veg containing the performances of the musical. Here is a screen grab of the project properties for the performances veg:

The video of the performances was created by a Sony AX100, so the project properties are set to match. Here is the MediaInfo analysis of the video file:

General
Complete name                            : E:\Theater\Annie movies\CTA performances\Sunday 10_29\C0001.MP4
Format                                   : XAVC
Codec ID                                 : XAVC (XAVC/mp42/iso2)
File size                                : 33.3 GiB
Duration                                 : 1 h 25 min
Overall bit rate mode                    : Variable
Overall bit rate                         : 55.5 Mb/s
Encoded date                             : UTC 2017-10-29 18:54:06
Tagged date                              : UTC 2017-10-29 18:54:06

Video
ID                                       : 1
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High@L5.1
Format settings                          : CABAC / 2 Ref Frames
Format settings, CABAC                   : Yes
Format settings, RefFrames               : 2 frames
Codec ID                                 : avc1
Codec ID/Info                            : Advanced Video Coding
Duration                                 : 1 h 25 min
Source duration                          : 1 h 25 min
Bit rate mode                            : Variable
Bit rate                                 : 53.7 Mb/s
Maximum bit rate                         : 60.0 Mb/s
Width                                    : 3 840 pixels
Height                                   : 2 160 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 29.970 (30000/1001) FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 0.216
Stream size                              : 32.2 GiB (97%)
Source stream size                       : 32.2 GiB (97%)
Encoded date                             : UTC 2017-10-29 18:54:06
Tagged date                              : UTC 2017-10-29 18:54:06
Color range                              : Limited
Color primaries                          : BT.709
Transfer characteristics                 : xvYCC
Matrix coefficients                      : BT.709

Audio
ID                                       : 2
Format                                   : PCM
Format settings                          : Big / Signed
Codec ID                                 : twos
Duration                                 : 1 h 25 min
Bit rate mode                            : Constant
Bit rate                                 : 1 536 kb/s
Channel(s)                               : 2 channels
Sampling rate                            : 48.0 kHz
Bit depth                                : 16 bits
Stream size                              : 942 MiB (3%)
Encoded date                             : UTC 2017-10-29 18:54:06
Tagged date                              : UTC 2017-10-29 18:54:06

Other
Type                                     : meta
Duration                                 : 1 h 25 min
Source duration                          : 5146141
Source frame count                       : 154230
Source stream size                       : 157931520
Stream size                              : 157931520

Here is a screen grab of how the same program page appears on the Vegas timeline for this performances veg:

I then rendered the performances veg using the standard DVD Architect widescreen template, with a CBR of 3450 (as noted above, I can probably use a 4000 bitrate but was being conservative until I knew how much other stuff I’d want to put on the DVD). Here is a screen grab of the same page in the final rendered output:

As you can see, this final rendered output is much softer, barely readable on my 17” inch computer monitor.

In case it matters, I am using Vegas Pro 14.0 (build 270) on Windows 10 Home (version 1803) with graphics acceleration turned off.

I appreciate any suggestions for how to make this text look sharp enough to be readable.

Of course, another option is to just type it all into media generator(s) of your choice, won’t be egsactly the same as the original but it will be clear.

Realize you are going from a resolution of 4000x5000 to 720 x 480.It will soften, now way around it. First, do not scan that high, there is no reason unless you are doing big zooms into the picture. Scan about 2x your final resolution so around 1440 x 960 (or equivalent based on your aspect). If you are not planning on any moves or zooms, scan at a matching resolution of 720 x whatever. And still realize, it will get soft. You are letting a video program downrez stills and that is not what a video program does best.

JN -- I did think of that but (a) it's a LOT of typing and (b) I don't think I could fully recreate the look of the original program, which includes some graphics.

daivid-tu -- I got the pdf from the person who created the program so that is the resolution they came to me in. Would it make sense to downscale the resolution in a graphics program like Gimp and then bring those smaller stills into Vegas?

Edit: the screen grabs below were uploaded using the forum uploader. When I try to view them in the context of my comment they appear on my screen so small as to be worthless.

Click on them. That will enlarge them.

If you want to see what is possible at DVD-Video resolution you could down-sample a program page of your program to 720x480 in your photo editing software. You might decide that it isn't going to work out as well as you might have imagined. I did.

You should set Full resolution rendering quality to Best though the difference may be marginal since most of the issue is probably not rendering quality but the low number of video pixels to scanned picture pixels the DVD resolution can accommodate.

"I appreciate any suggestions for how to make this text look sharp enough to be readable."

One way would be to put less text per DVD screen by resizing your source files in a photo editor to show just the scenes in play at the time and do a credit roll or chop the scenes and display them as appropriate in time with the play.

Note: Mine won't look any better than your since I used your rendered sample as my source file.